Optical element, optical head, optical information recording/reproduction device, computer, video recording device, video reproduction device, server, and car navigation system

ABSTRACT

The present invention provides a first light source ( 21 ) that emits light of a first wavelength, that at least either records onto or reproduces information from an information recording medium ( 30 ), a light source ( 22 ) that emits light of a second wavelength that records onto or reproduces information from an information recording medium ( 33 ), a light source ( 23 ) that emits light of a third wavelength that records onto or reproduces information from an information recording medium ( 23 ), focusing means, an optical element ( 28 ) that passes light of the first wavelength and diffracts light of the second and third wavelengths, wherein the optical element ( 28 ) is an optical element in which grooves are formed in a substrate, wherein the expression:
 
380 nm≦( n −1)× d≦ 420 nm
 
is satisfied, where n is a refractive index of the substrate at a wavelength of 400 nm, and d (nm) is a depth per step of the grooves, and wherein the grooves are formed in two steps of depth d and depth  2   d.

TECHNICAL FIELD

The present invention relates to optical information recording andreproduction apparatuses, computers, image recording devices, imagereproduction devices, servers and car navigation systems for performinginformation recording, reproduction or erasure of information oninformation recording media such as optical disks and optical cards, andto optical elements, optical heads and liquid crystal elements used inthese devices.

BACKGROUND ART

Optical memory technology that uses optical disks as high-density,large-volume memory media gradually is being applied widely to andentering general use in digital audio disks, video disks, document filedisks and also data files. To successfully achieve recording onto andreproduction of information from an optical disk with high reliabilityvia a minutely narrowed light beam, there is a need for a focusingfunction forming a minute spot at the diffraction limit, focus controland tracking control of the optical system, and a pit signal(“information signal”) detection function.

With recent advances in optical system design technology and theshortening of wavelengths of the semiconductor lasers serving as lightsources, the development of optical disks containing volumes of memoryat greater than conventional densities is progressing. As an approach tohigher densities, increasing the optical disk side numerical aperture(NA) of a focusing optical system that minutely stops down a light beamonto an optical disk has been investigated. A problem that occurs atthis time is that there is an increase in aberration caused by aninclination of the disk in relation to the light axis (what is known as“tilt”). When the NA is made large, the aberration caused by tiltincreases. It is possible to prevent this by reducing the thickness(substrate thickness) of the transparent substrate of the optical disk.

A Compact Disc (CD), which can be considered a first generation opticaldisk, is used with a light source emitting infrared light (a wavelengthλ3 is 780 nm to 820 nm) and an objective lens with an NA of 0.45, andhas a substrate thickness of approximately 1.2 mm. A Digital VersatileDisc (DVD), which can be considered a second generation optical disk, isused with a light source emitting red light (a wavelength λ2 is 630 nmto 680 nm) and an objective lens with an NA of 0.6, and has a substratethickness of approximately 0.6 mm. And, a system has been proposed inwhich a third generation optical disk is used with a light source thatemits blue light (a wavelength λ1 is 380 nm to 420 nm) and an objectivelens with an NA of 0.85, the disk having a substrate thickness of 0.1mm.

It should be noted that in this specification, the substrate thicknessmeans the thickness of the transparent substrate from the face at whicha light beam is incident on the optical disk (or optical recordingmedium) to the information recording surface.

Thus, the thickness of the substrate of optical disks becomes thinnerwith increasing recording density. From the standpoint of economics andthe space occupied by the device, it is desirable that a single opticalinformation recording and reproduction apparatus is capable of recordingand reproducing optical disks of different substrate thickness andrecording density. For this purpose, there is a need for an optical headdevice that is provided with a focusing optical system that is capableof focusing a light beam up to the diffraction limit onto optical disksof different substrate thicknesses.

An example of a device that records and reproduces information from bothDVD and CD optical disks (information recording media) is proposed inthe Patent Document 1 described below. As a first conventional example,this content is described simply using FIGS. 58 to 60. FIG. 58 is astructural overview of an optical head 300. FIG. 58A shows the manner inwhich information is recorded onto or reproduced from a DVD and FIG. 58Bshows the manner in which information is recorded onto or reproducedfrom a CD. It contains a red semiconductor laser 301 that emits light ofa wavelength of 635 nm to 650 nm, and an infrared semiconductor laser302 that emits light of a wavelength of 780 nm.

When reproducing a DVD 308, which is a second information recordingmedium, the light emitted from the red semiconductor laser 301 passesthrough a wavelength selecting prism 303, and is converted to collimatedlight by a collimator lens 304. The light that was converted tocollimated light is reflected by a beam splitter 305, passes through adichroic hologram 306, is converted to convergent light by an objectivelens 307, and is irradiated onto the DVD 308. The light that wasreflected by the DVD 308 again passes through the objective lens 307 andthe dichroic hologram 306, passes through the beam splitter 305, isconverted to convergent light by a detecting lens 309, and is focusedonto a photodetector 310.

When reproducing a CD 311, which is a third information recordingmedium, the light emitted from the infrared semiconductor laser 302 isreflected by the wavelength selecting prism 303, and is converted tocollimated light by a collimator lens 304. The light that was convertedto collimated light is reflected by a beam splitter 305, is diffractedby the dichroic hologram 306, is converted to convergent light by anobjective lens 307, and is irradiated onto the CD 311. The light thatwas reflected by the CD 311 again passes through the objective lens 307and the dichroic hologram 306, passes through the beam splitter 305, isconverted to convergent light by the detecting lens 309, and is focusedonto the photodetector 310.

Spherical aberration caused by the difference in substrate thickness ofDVDs and CDs is corrected by the dichroic hologram 306. FIG. 59 is across-sectional view of the dichroic hologram 306. Grooves of depth d, 2d and 3 d are arranged in that order on the surface of the dichroichologram 306. The depth d is determined such that,d =λ1/(n1−1)where λ1 is the wavelength of the red semiconductor laser and n1 is therefractive index of the dichroic hologram 306 at the wavelength λ1. Inthis way, the transmittance of the light of wavelength λ1, increaseswithout diffracting the light.

Here, the wavelength of light emitted from the infrared semiconductorlaser is λ2, and the refractive index of the dichroic hologram 306 atthe wavelength λ2 is n2. FIG. 60A shows the wavefront after the light ofwavelength λ2 has passed the dichroic hologram 306, in which,d×(n2−1)/λ2=0.75.In this case, a phase shift of 0.75 times the wavelength occurs perstep. As phase shifts of greater than one can be ignored, FIG. 60B showsa wavefront that is re-written, based only on that portion to the rightof the decimal point. This wavefront becomes first order diffractionlight, which has a high diffraction efficiency at one side.

Furthermore, in the non-Patent Document 1 described below an example isgiven of a device for reproducing information on CDs, DVDs and ultrahigh density optical disks. This is briefly explained using FIGS. 61 and62 as a second conventional example. FIG. 61 is a structural overviewshowing an optical head.

Collimated light emitted from an optical system 201 that contains a bluelight source of wavelength λ1=405 nm passes through prisms 204, 205 anda phase plate 206, which will be explained later, is focused by anobjective lens 207, and is irradiated onto an information recordingsurface of an optical disk 208 (an ultra high density optical disk)whose substrate thickness is 0.1 mm.

The light that was reflected by the optical disk 208 returns back alongthe travel path and is detected by a photodetector of the optical system201. The diverging light that is emitted by an optical system 202 thatcontains a source of red light of wavelength λ2=650 nm is reflected bythe prism 204, passes through the prism 205 and the phase plate 206, isfocused by the objective lens 207 and is irradiated onto an informationrecording surface of an optical disk 209 (DVD), whose substratethickness is 0.6 mm.

The light that was reflected from the optical disk 209 returns backalong the travel path, and is detected by a photodetector of the opticalsystem 202. The diverging light emitted by an optical system 203, whichhas a source of infrared light of a wavelength λ3=780 nm is reflected bythe prism 205, passes through the phase plate 206, is focused by theobjective lens 207, and is irradiated onto an information recordingsurface of an optical disk 210 (CD), whose substrate thickness is 1.2mm. The light that was reflected by the optical disk 210 returns backalong the travel path, and is detected by a photodetector of the opticalsystem 203.

The objective lens 207 is designed so as to handle substrate thicknessesof 0.1 mm, and spherical aberration occurs in CDs and DVDs because ofthe difference in substrate thickness. Correction of this sphericalaberration occurs due to the degree of divergence of the diverging lightthat is emitted by the optical system 202 and optical system 203, anddue to the phase plate 206. Different spherical aberration is generatedwhen divergent light is incident on the objective lens, so it ispossible to cancel out spherical aberration caused by the difference insubstrate thickness by this new spherical aberration.

The degree of divergence of the diverging light is set such thatspherical aberration is a minimum. Spherical aberration caused by thediverging light cannot be completely corrected, and higher orderspherical aberrations (principally fifth order spherical aberrations)remain. These fifth order spherical aberrations are corrected by thephase plate 206.

FIG. 62 shows a surface (FIG. 62A) and a lateral view (FIG. 62B) of thephase plate 206. If the refractive index at the wavelength λ1 is definedas n1, and h=λ1/(n1−1), then the phase plate 206 is constituted by phaseshift steps 206 a of height h and height 3h. The height h generates aphase shift of 1λ (where λ is the wavelength that is used) in the lightof wavelength λ1, however this does not affect the phase distributionand there is no impediment to recording or reproduction of the opticaldisk 208.

On the other hand, if the refractive index of the phase plate 206 at thewavelength λ2 is n2, then a phase shift of the light of wavelength λ2 ofh/λ2×(n2−1)=0.625 λ is generated. Furthermore, if the refractive indexof the phase plate 206 at the wavelength λ3 is n3, then a phase shift ofthe light of wavelength λ3 of h/λ3×(n3−1)=0.52 λ is generated. Inrelation to DVDs and CDs, this wave shift is used to convert thewavefronts, and the remaining fifth order spherical aberrations arecorrected.

Moreover, the Patent Document 2 described below proposes a method forreproducing information using an objective lens that is capable ofrecording and reproducing ultra high density optical disks, and twoobjective lenses that are capable of reproducing CDs and DVDs. This isdescribed briefly as a third conventional example, using FIG. 63.

A lens holder 233 is provided with an objective lens 231 that is usedwhen recording onto and replaying from ultra high density optical disks,an objective lens 232 that is used when reproducing DVDs and CDs, anddrive coils 234, and is suspended by wires 236 from a fixed portion 237.

A magnetic circuit is constituted by a magnet 238 and a yoke 239. Anelectromagnetic force is caused by the flow of electric current throughthe drive coil 234, and the objective lenses 231 and 232 are driven inthe focusing direction and the tracking direction. In the thirdconventional example, which of the objective lenses 231 and 232 is useddepends on the optical disk to be recorded and reproduced.

Furthermore, as a technique for correcting chromatic aberration, achromatic aberration correcting hologram is proposed in the PatentDocument 3 described below, in which the cross-sectional shape of theoptical element is saw tooth shaped, wherein light of a first wavelengthλ1 is corrected using second order diffracted light, and light of asecond wavelength λ2 is corrected using first order diffracted light.

However, in the optical head of the first conventional example, whenlight is irradiated onto optical disks that have widely differentsubstrate thicknesses, such as a substrate thickness of 1.2 mm and asubstrate thickness of 0.1 mm, there is the problem that the distancebetween the disk and the objective lens changes significantly, themovable range of the actuator increases, and the head becomes large.Moreover, there is the problem that in order to detect the light thatcorresponds to the three types of light sources, the number of signalwires increases and the width of the flexible cable that connects theoptical head and the optical disk drive is wider.

Furthermore, in the optical disk device according to the secondconventional example, since the light is incident on the objective lensas divergent light when reproducing CDs and DVDs, there is the problemthat when the objective lens is driven in the tracking direction, alarge coma aberration is generated and the optical disks cannot befavorably reproduced.

Furthermore, in the optical disk device of the third conventionalexample, because the objective lenses 231 and 232 are lined up in atangential direction (y direction) and the objective lens 231 isarranged such that it is positioned on a straight line in the trackingdirection (x direction) that passes through a rotational center O of theoptical disk, there is the problem that DVDs and CDs that use theobjective lens 232 cannot use the differential push-pull (DPP) method orthe three beam method, which are common tracking detection methods. Thisproblem is described using FIG. 64. The DPP method or the three beammethod use a main spot for reproduction, and two sub spots for trackingdetection. A main spot 232 a of the objective lens 232 shown in FIG. 63is in a spot position 150 a shown in FIG. 64. The subspots are inpositions 150 b and 150 c, and are set at an optimal angle θ₀ withrespect to a reproduction track 153.

The spots move in the x-direction in accordance with the seek operationof the optical head, and the spot positions change to 151 a, 151 b and151 c. Because the spot positions 150 a and 151 a are not on thestraight line that passes through the axis of rotation O of the opticaldisks in the x-direction, the angle θ₀ changes to θ₁ due to the seekoperation of the optical head. That is to say, in the configuration ofthe third conventional example, there is the problem that trackingcontrol cannot be carried out reliably.

-   Patent Document 1-   JP H9-306018A-   Patent Document 2-   JP H11-120587A-   Patent Document 3-   JP 2001-60336-   Non-Patent Document 1-   Session We-C-05 of ISOM 2001 (p30 of the proceedings)

DISCLOSURE OF INVENTION

It is an object of the present invention to solve the foregoingconventional problems, and to provide optical elements, optical heads,optical information recording and reproduction apparatuses, computers,image recording devices, image reproduction devices, servers andnavigation systems that can reliably record information onto andreproduce from a plurality of information recording media whosesubstrate thicknesses are different.

In order to achieve this object, a first optical element of the presentinvention comprises a substrate in which grooves are formed;

-   -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves; and    -   wherein the grooves are formed in two steps of depth d and depth        2 d.

A second optical element of the present invention comprises a substratein which grooves are formed;

-   -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves; and    -   wherein the grooves are formed in four steps of depth d, depth 2        d, depth 3 d and depth 4 d.

A first optical head of the present invention comprises a first lightsource that emits light of a first wavelength that at least eitherrecords onto or reproduces information from a first informationrecording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   focusing means for focusing light that is emitted from the first        light source and from the second light source;    -   an optical element that passes light of the first wavelength and        diffracts light of the second wavelength; and    -   photodetecting means for detecting light of the first wavelength        and light of the second wavelength;    -   wherein light of the first wavelength and light of the second        wavelength pass through the optical element, after which they        are focused by the focusing means and are irradiated onto the        information recording media;    -   wherein the optical element is an optical element in which        grooves are formed in a substrate;    -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves;    -   wherein the grooves are formed in two steps of depth d and depth        2 d; and    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media.

A second optical head of the present invention comprises a first lightsource that emits light of a first wavelength, that at least eitherrecords onto or reproduces information from a first informationrecording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   focusing means for focusing light that is emitted from the first        light source and from the second light source;    -   an optical element that passes light of the first wavelength and        diffracts light of the second wavelength; and    -   photodetecting means for detecting light of the first wavelength        and light of the second wavelength;    -   wherein light of the first wavelength and light of the second        wavelength pass through the optical element, after which they        are focused by the focusing means and are irradiated onto the        information recording media;    -   wherein the optical element is an optical element in which        grooves are formed in a substrate;    -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves;    -   wherein the grooves are formed in four steps of depth d, depth 2        d, depth 3 d and depth 4 d; and    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media.

A third optical head of the present invention comprises a first lightsource that emits light of a first wavelength, that at least eitherrecords onto or reproduces information from a first informationrecording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a third light source that emits light of a third wavelength,        that at least either records onto or reproduces information from        a third information recording medium;    -   focusing means for focusing light that is emitted from the first        light source, from the second light source and from the third        light source;    -   a first optical element that passes light of the first        wavelength and diffracts light of the second wavelength and        light of the third wavelength;    -   photodetecting means for detecting light of the first        wavelength, light of the second wavelength and light of the        third wavelength;    -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        optical element, after which they are focused by the focusing        means and are irradiated onto the information recording media;    -   wherein the first optical element is an optical element in which        grooves are formed in a substrate;    -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves;    -   wherein the grooves are formed in two steps of depth d and depth        2 d; and    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media.

A fourth optical head of the present invention comprises a first lightsource that emits light of a first wavelength, that at least eitherrecords onto or reproduces information from a first informationrecording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a third light source that emits light of a third wavelength,        that at least either records onto or reproduces information from        a third information recording medium;    -   focusing means for focusing light that is emitted from the first        light source, from the second light source and from the third        light source;    -   a first optical element that passes light of the first        wavelength and diffracts light of the second wavelength and the        third wavelength; and    -   photodetecting means for detecting light of the first        wavelength, light of the second wavelength and light of the        third wavelength;    -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        optical element, after which they are focused by the focusing        means and are irradiated onto the information recording media;    -   wherein the first optical element is an optical element in which        grooves are formed in a substrate;    -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves;    -   wherein the grooves are formed in four steps of depth d, depth 2        d, depth 3 d and depth 4 d; and    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media.

A first optical information recording and reproduction apparatus of thepresent invention comprises an optical head that includes;

-   -   a first light source that emits light of a first wavelength,        that at least either records onto or reproduces information from        a first information recording medium;    -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   focusing means for focusing light that is emitted from the first        light source and from the second light source;    -   an optical element that passes light of the first wavelength and        diffracts light of the second wavelength; and    -   photodetecting means for detecting light of the first wavelength        and light of the second wavelength,    -   and further comprises:    -   moving means for moving the information recording medium and the        optical head relative to each other;    -   wherein light of the first wavelength and light of the second        wavelength pass through the optical element, after which they        are focused by the focusing means and are irradiated onto the        information recording media;    -   wherein the optical element is an optical element in which        grooves are formed in a substrate;    -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves;    -   wherein the grooves are formed in two steps of depth d and depth        2 d; and    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media.

A second optical information recording and reproduction apparatus of thepresent invention comprises an optical head that includes;

-   -   a first light source that emits light of a first wavelength,        that at least either records onto or reproduces information from        a first information recording medium;    -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   focusing means for focusing light that is emitted from the first        light source and from the second light source;    -   an optical element that passes light of the first wavelength and        diffracts light of the second wavelength; and    -   photodetecting means for detecting light of the first wavelength        and light of the second wavelength,    -   and further comprises:    -   moving means for moving the information recording medium and the        optical head relative to each other;    -   wherein light of the first wavelength and light of the second        wavelength pass through the optical element, after which they        are focused by the focusing means and are irradiated onto the        information recording media;    -   wherein the optical element is an optical element in which        grooves are formed in a substrate;    -   wherein the expression:        380 (nm)≦(n−1)×d≦420 (nm)        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves;    -   wherein the grooves are formed in four steps of depth d, depth 2        d, depth 3 d and depth 4 d; and    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media.

A third optical information recording and reproduction apparatus of thepresent invention comprises an optical head that includes;

-   -   a first light source that emits light of a first wavelength,        that at least either records onto or reproduces information from        a first information recording medium;    -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a third light source that emits light of a third wavelength,        that at least either records onto or reproduces information from        a third information recording medium;    -   focusing means for focusing light that is emitted from the first        light source, from the second light source and from the third        light source;    -   a first optical element that passes light of the first        wavelength and diffracts light of the second wavelength and        light of the third wavelength; and    -   photodetecting means for detecting light of the first        wavelength, light of the second wavelength and light of the        third wavelength;    -   and further comprises:    -   moving means for moving the information recording medium and the        optical head relative to each other;    -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        optical element, after which they are focused by the focusing        means and are irradiated onto the information recording media;    -   wherein the first optical element is an optical element in which        grooves are formed in a substrate;    -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves;    -   wherein the grooves are formed in two steps of depth d and depth        2 d; and    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media.

A fourth optical information recording and reproduction apparatus of thepresent invention comprises an optical head that includes;

-   -   a first light source that emits light of a first wavelength,        that at least either records onto or reproduces information from        a first information recording medium;    -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a third light source that emits light of a third wavelength,        that at least either records onto or reproduces information from        a third information recording medium;    -   focusing means for focusing light that is emitted from the first        light source, from the second light source and from the third        light source;    -   a first optical element that passes light of the first        wavelength and diffracts light of the second wavelength and        light of the third wavelength; and    -   photodetecting means for detecting light of the first        wavelength, light of the second wavelength and light of the        third wavelength;    -   and further comprises:    -   moving means for moving the information recording medium and the        optical head relative to each other;    -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        optical element, after which they are focused by the focusing        means and are irradiated onto the information recording media;    -   wherein the first optical element is an optical element in which        grooves are formed in a substrate;    -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves;    -   wherein the grooves are formed in four steps of depth d, depth 2        d, depth 3 d and depth 4 d; and    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media.

A third optical element of the present invention comprises a substrate,in which steps are formed protruding from a flat surface thereof;

-   -   wherein the expression:        760 nm≦(n−1)×d≦840 nm        is satisfied when a refractive index of the substrate at a        wavelength of 400 nm is n, and a height (nm) of one step is d;        and    -   wherein the height of the steps is an integer multiple of d.

A fifth optical head of the present invention comprises a first lightsource that emits light of a first wavelength that is in a range of 380nm to 420 nm and that at least either records onto or reproducesinformation from a first information recording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   an optical element that passes light of the first wavelength,        and converts the phase of light of the second wavelength;    -   focusing means for focusing light of the first wavelength and        light of the second wavelength onto the information recording        medium;    -   detecting means for detecting light of the first wavelength and        light of the second wavelength;    -   wherein the optical element is an optical element comprising a        substrate, in which steps are formed protruding from a flat        surface thereof; and    -   wherein the expression:        760 nm≦(n−1)×d≦840 nm        is satisfied when a refractive index of the substrate at a        wavelength of 400 nm is n, and a height (nm) of one step is d.

A sixth optical head of the present invention comprises a first lightsource that emits light of a first wavelength that is in a range of 380nm to 420 nm and that at least either records onto or reproducesinformation from a first information recording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   an optical element that passes light of the first wavelength,        and converts the phase of light of the second wavelength;    -   focusing means for focusing light of the first wavelength and        light of the second wavelength onto the information recording        medium; and    -   detecting means for detecting light of the first wavelength and        light of the second wavelength;    -   wherein the position of the second light source is set closer to        the focusing means than a position at which the aberration at        the information recording surface of the second information        recording medium, when the optical element is not present, is at        a minimum.    -   wherein the optical element is an optical element comprising a        substrate, in which steps are formed protruding from a flat        surface thereof; and    -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied when a refractive index of the substrate at a        wavelength of 400 nm is n, and a height (nm) of one step is d.

A seventh optical head of the present invention comprises a first lightsource that emits light of a first wavelength that is in a range of 380nm to 420 nm and that at least either records onto or reproducesinformation from a first information recording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   an optical element that passes light of the first wavelength,        and converts the phase of light of the second wavelength;    -   focusing means for focusing light of the first wavelength and        light of the second wavelength onto the information recording        medium; and    -   detecting means for detecting light of the first wavelength and        light of the second wavelength;    -   wherein the position of the second light source is set further        from the focusing means than a position that is substantially        midway between the position of that light source at which the        aberration at the information recording surface of the second        information recording medium when the optical element is not        present is at a minimum, and the position of that light source        at which light of the second wavelength that is incident on the        focusing means is collimated light.    -   wherein the optical element is an optical element comprising a        substrate, in which steps are formed protruding from a flat        surface thereof; and    -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied when a refractive index of the substrate at a        wavelength of 400 nm is n, and a height (nm) of one step is d.

An eighth optical head of the present invention comprises a a firstlight source that emits light of a first wavelength that is in a rangeof 380 nm to 420 nm and that at least either records onto or reproducesinformation from a first information recording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   an optical element that passes light of the first wavelength,        and converts the phase of light of the second wavelength;    -   focusing means for focusing light of the first wavelength and        light of the second wavelength onto the information recording        medium; and    -   detecting means for detecting light of the first wavelength and        light of the second wavelength;    -   wherein light of the second wavelength that is incident on the        focusing means is collimated light;    -   wherein the optical element is an optical element comprising a        substrate, in which steps are formed protruding from a flat        surface thereof; and    -   wherein the expression:        380 nm≦(n−1)×d≦420 nm        is satisfied when a refractive index of the substrate at a        wavelength of 400 nm is n, and a height (nm) of one step is d.

A ninth optical head of the present invention comprises a first lightsource that emits light of a first wavelength that is in a range of 380nm to 420 nm and that at least either records onto or reproducesinformation from a first information recording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a third light source that emits light of a third wavelength,        that at least either records onto or reproduces information from        a third information recording medium;    -   an optical element that passes light of the first wavelength and        light of the third wavelength, and converts the phase of light        of the second wavelength;    -   focusing means for focusing light of the first wavelength, light        of the second wavelength and light of the third wavelength onto        the information recording medium; and    -   detecting means for detecting light of the first wavelength,        light of the second wavelength and light of the third        wavelength;    -   wherein the optical element is an optical element comprising a        substrate, in which steps are formed protruding from a flat        surface thereof; and    -   wherein the expressions:        760 nm≦(n1−1)×d≦840 nm        and        −10 nm<λ1/(n1−1)−λ3/(n3−1)/2<10 nm        are satisfied when a refractive index of the optical element at        the wavelength of 400 nm is n, the third wavelength is λ3 (nm),        a refractive index of the optical element at the wavelength λ3        is n3, and a height (nm) of one step is d.

A tenth optical head of the present invention comprises a first lightsource that emits light of a first wavelength that is in a range of 380nm to 420 nm and that at least either records onto or reproducesinformation from a first information recording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a third light source that emits light of a third wavelength,        that at least either records onto or reproduces information from        a third information recording medium;    -   an optical element that passes light of the first wavelength and        light of the third wavelength, and changes the phase of light of        the second wavelength;    -   a liquid crystal element that passes light of the first        wavelength and light of the second wavelength, and diffracts        light of the third wavelength;    -   focusing means for focusing light of the first wavelength, light        of the second wavelength and light of the third wavelength onto        the information recording medium; and    -   detecting means for detecting light of the first wavelength,        light of the second wavelength and light of the third        wavelength;    -   wherein the optical element is an optical element comprising a        substrate, in which steps are formed protruding from a flat        surface thereof;    -   wherein the expression:        700 nm≦(n−1)×d≦840 nm        is satisfied when a refractive index of the substrate at a        wavelength of 400 nm is n, and a height (nm) of one step is d;        and    -   wherein the liquid crystal element comprises:    -   a substrate that has a relief-shaped hologram pattern;    -   a first transparent electrode, which is formed on the        relief-shaped hologram pattern; and    -   a second transparent electrode that is arranged opposite the        first transparent electrode to sandwich the liquid crystal;    -   wherein the liquid crystal element passes light of the first        wavelength and light of the second wavelength, and diffracts        light of the third wavelength by controlling a voltage that is        applied to the first transparent electrode and the second        transparent electrode.

An eleventh optical head of the present invention comprises a firstlight source that emits light of a first wavelength, that at leasteither records onto or reproduces information from a first informationrecording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a third light source that emits light of a third wavelength,        that at least either records onto or reproduces information from        a third information recording medium;    -   focusing means for focusing light that is emitted from the first        light source, from the second light source and from the third        light source;    -   a first optical element that passes light of the first        wavelength and diffracts light of the second wavelength and        light of the third wavelength;    -   photodetecting means for detecting light of the first        wavelength, light of the second wavelength, and light of the        third wavelength;    -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        optical element, after which they are focused by the focusing        means and are irradiated onto the information recording media;        and    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media.

A twelfth optical head of the present invention comprises a first lightsource that emits light of a first wavelength, that at least eitherrecords onto or reproduces information from a first informationrecording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a third light source that emits light of a third wavelength,        that at least either records onto or reproduces information from        a third information recording medium;    -   focusing means for focusing light that is emitted from the first        light source, from the second light source and from the third        light source;    -   photodetecting means for detecting light of the first        wavelength, light of the second wavelength, and light of the        third wavelength;    -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        optical element, after which they are focused by the focusing        means and are irradiated onto the information recording media;    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media; and    -   wherein, when a distance between the surface of the first        information recording medium on the focusing means side, and the        tip of the focusing means on the side of the first information        recording medium is WD1 when light of the first wavelength is        irradiated onto the first information recording medium, and    -   a distance between the surface of the second information        recording medium on the focusing means side, and the tip of the        focusing means on the side of the second information recording        medium is WD2 when light of the second wavelength is irradiated        onto the second information recording medium, and    -   a distance between the surface of the third information        recording medium on the focusing means side, and the tip of the        focusing means on the side of the third information recording        medium is WD3 when light of the third wavelength is irradiated        onto the third information recording medium,    -   a difference between the maximum value and the minimum value of        WD1, WD2 and WD3 is smaller than the maximum value of the        diameter of the focusing means.

A thirteenth optical head of the present invention comprises a firstlight source that emits light of a first wavelength, that at leasteither records onto or reproduces information from a first informationrecording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a third light source that emits light of a third wavelength,        that at least either records onto or reproduces information from        a third information recording medium;    -   focusing means for focusing light that is emitted from the first        light source, from the second light source and from the third        light source;    -   photodetecting means for detecting light of the first        wavelength, light of the second wavelength, and light of the        third wavelength;    -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        optical element, after which they are focused by the focusing        means and are irradiated onto the information recording media;    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media; and    -   wherein, when a distance between the surface of the first        information recording medium on the focusing means side, and the        tip of the focusing means on the side of the first information        recording medium is WD1 when light of the first wavelength is        irradiated onto the first information recording medium, and    -   a distance between the surface of the second information        recording medium on the focusing means side, and the tip of the        focusing means on the side of the second information recording        medium is WD2 when light of the second wavelength is irradiated        onto the second information recording medium, and    -   a distance between the surface of the third information        recording medium on the focusing means side, and the tip of the        focusing means on the side of the third information recording        medium is WD3 when light of the third wavelength is irradiated        onto the third information recording medium,    -   WD1, WD2 and WD3 are substantially equivalent.

A fourteenth optical head of the present invention comprises a lightsource that emits light that at least either records onto or reproducesinformation from an information recording medium;

-   -   focusing means for focusing light that is emitted from the light        source; and    -   photodetecting means for detecting the light;    -   wherein the light is focused by the focusing means and is        irradiated onto the information recording media;    -   wherein the detecting means detects the light that is at least        either reflected or diffracted by the information recording        media; and    -   further comprises converter for converting a plurality of        signals, which are received in parallel, that are output from        the photodetecting means into a serial signal.

A fifth optical information recording and reproduction apparatuscomprises an optical head that includes;

-   -   a first light source that emits light of a first wavelength,        that at least either records onto or reproduces information from        a first information recording medium;    -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a third light source that emits light of a third wavelength,        that at least either records onto or reproduces information from        a third information recording medium;    -   focusing means for focusing light that is emitted from the first        light source, from the second light source and from the third        light source;    -   a first optical element that passes light of the first        wavelength and diffracts light of the second wavelength and        light of the third wavelength; and    -   photodetecting means for detecting light of the first        wavelength, light of the second wavelength, and light of the        third wavelength,    -   and further comprises:    -   moving means for moving the information recording medium and the        optical head relative to each other;    -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        optical element, after which they are focused by the focusing        means and are irradiated onto the information recording media;        and    -   wherein the photodetecting means detects light that is at least        either reflected or diffracted by the information recording        media.

A fifteenth optical head of the present invention comprises firstfocusing means and second focusing means for irradiating light onto theinformation recording medium;

-   -   wherein the first focusing means and the second focusing means        are lined up in the tracking direction;    -   wherein the first focusing means is positioned on the inner        circumference side of the information recording medium, and the        second focusing means is positioned on the outer circumference        side of the information recording medium;    -   wherein the outside diameter of the first focusing means is less        than the outside diameter of the second focusing means, and the        second focusing means can reproduce information at the inner        most circumference of the information recording medium when a        rotating system, which rotates the information recording medium,        and the optical head are in close proximity.

A sixteenth optical head of the present invention is an optical headthat at least either records onto or reproduces information from atleast three information recording media that have different substratethickness;

-   -   wherein the optical head contains first focusing means and        second focusing means for irradiating light onto the information        recording medium; and    -   wherein the first focusing means irradiates light onto a first        information recording medium whose substrate thickness is most        thick, and the second focusing means irradiates light onto the        information recording media, excluding the first information        recording medium.

A seventeenth optical head of the present invention is an optical headthat at least either records onto or reproduces information from aplurality of information recording media that have different substratethickness, comprising:

-   -   a plurality of focusing means that irradiate light onto the        plurality of information recording medium; and    -   a movable body that is capable of moving in the focus direction        and in the tracking direction;    -   wherein the focusing means that irradiates light onto the        information recording medium whose substrate thickness is the        thinnest is positioned substantially in the center of the        movable body, and the plurality of focusing means are mounted on        the movable body, lined up in the tracking direction.

An eighteenth optical head of the present invention comprises a firstlight source that emits light of a first wavelength, that at leasteither records onto or reproduces information from a first informationrecording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   a focusing means for focusing light of the first wavelength and        light of the second wavelength onto the information recording        medium; and    -   detecting means for detecting light of the first wavelength and        light of the second wavelength,    -   wherein light of the second wavelength is irradiated onto the        first information recording medium to detect the tilt of the        first information recording medium.

A nineteenth optical head of the present invention comprises a firstlight source that emits light of a first wavelength, that at leasteither records onto or reproduces information from a first informationrecording medium;

-   -   a second light source that emits light of a second wavelength,        that at least either records onto or reproduces information from        a second information recording medium;    -   first focusing means for focusing light of the first wavelength        onto the first information recording medium;    -   second focusing means for focusing light of the second        wavelength onto the second information recording medium; and    -   detecting means for detecting light of the first wavelength and        light of the second wavelength;    -   wherein light of the second wavelength is irradiated onto the        first information recording medium to detect the tilt of the        first information recording medium.

A liquid crystal element of the present invention comprises a substratethat has a relief-shaped hologram pattern;

-   -   a first transparent electrode, which is formed on the        relief-shaped hologram pattern; and    -   a second transparent electrode that is arranged opposite the        first transparent electrode to sandwich the liquid crystal;    -   wherein it is possible to change between diffracting and passing        for the light incident in the liquid crystal element by        controlling a voltage that is applied to the first transparent        electrode and the second transparent electrode.

A sixth optical information recording and reproduction apparatus of thepresent invention comprises any of the fifth to tenth optical heads, orthe fifteenth to nineteenth optical heads; and

-   -   moving means for moving the information recording media and the        optical head relative to each other.

A computer of the present invention comprises an optical informationrecording and reproduction apparatus, which includes any of the opticalheads, as an external storage device.

An image recording device of the present invention comprises an opticalinformation recording and reproduction apparatus that includes any ofthe optical heads, wherein it can at least record moving images fromamong recording moving images onto and reproducing moving images from aninformation recording medium.

An image reproduction device of the present invention comprises anoptical information recording and reproduction apparatus that includesany of the optical head, wherein it reproduces images from aninformation recording medium.

A server of the present invention comprises an optical informationrecording and reproduction apparatus, which includes any of the opticalheads, as an external storage device.

A car navigation system of the present invention comprises an opticalinformation recording and reproduction apparatus, which includes any ofthe optical heads, as an external storage device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a structural diagram showing how a high density optical diskis recorded and reproduced according to the first embodiment of thepresent invention.

FIG. 1B is a structural diagram showing how a DVD is recorded andreproduced according to the first embodiment of the present invention.

FIG. 1C is a structural diagram showing how a CD is recorded andreproduced according to the first embodiment of the present invention.

FIG. 2A is a view of an upper surface of a dichroic hologram used in thefirst embodiment of the present invention.

FIG. 2B is a view of a rear surface of the dichroic hologram used in thefirst embodiment of the present invention.

FIG. 3 is a cross-sectional view of the dichroic hologram used in thefirst embodiment of the present invention.

FIG. 4A is a schematic view of wavefronts after light of wavelength λ2has passed through the dichroic hologram used in the first embodiment ofthe present invention.

FIG. 4B is a schematic diagram of the wavefronts that are calculated byignoring the integer portions of the wavelength of the wavefronts inFIG. 4A.

FIG. 5 is a conceptual diagram showing the diffraction efficiency oflight that is diffracted by the dichroic hologram used in the firstembodiment of the present invention.

FIG. 6A is a schematic view of a wavefront of the light of wavelength λ3after it has passed through the dichroic hologram used in the firstembodiment of the present invention.

FIG. 6B is a schematic view of the wavefront of FIG. 6A that iscalculated ignoring the integer portion of the wavelength.

FIG. 7 is a cross-sectional view of a separate dichroic hologram to thatused in the first embodiment of the present invention.

FIG. 8A is a schematic view of a wavefront of the light of wavelength λ2after it has passed through the dichroic hologram used in the firstembodiment of the present invention.

FIG. 8B is a schematic view of the wavefront of FIG. 8A that iscalculated ignoring the integer portion of the wavelength.

FIG. 8C is a schematic view of a wavefront of the light of wavelength λ3after it has passed through the dichroic hologram used in the firstembodiment of the present invention.

FIG. 8D is a schematic view of the wavefront of FIG. 8C that iscalculated ignoring the integer portion of the wavelength.

FIG. 9A is a conceptual diagram showing the diffraction efficiency ofthe light that is diffracted by the dichroic hologram that is used inthe first embodiment of the present invention.

FIG. 9B is a conceptual diagram showing the transmittance of the lightthat is diffracted by the dichroic hologram that is used in the firstembodiment of the present invention.

FIG. 10 is a schematic view showing the principal directions of thelight that is diffracted by the dichroic hologram that is used in thefirst embodiment of the present invention.

FIG. 11 is a structural diagram of an optical disk drive according tothe first embodiment of the present invention.

FIG. 12A is a schematic view of the optical disk drive according to thefirst embodiment of the present invention when recording onto andreproducing information from a disk, when the distance between the diskand focusing means is WD1.

FIG. 12B is a schematic view of the optical disk drive according to thefirst embodiment of the present invention when recording onto andreproducing information from a disk, when the distance between the diskand focusing means is WD2.

FIG. 12C is a schematic view of the optical disk drive according to thefirst embodiment of the present invention when recording onto andreproducing information from a disk, when the distance between the diskand focusing means is WD3.

FIG. 13A is a schematic view of a conventional optical disk drive whenrecording onto and reproducing information from a disk, when thedistance between the disk and focusing means is WDa.

FIG. 13B is a schematic view of the conventional optical disk drive whenrecording onto and reproducing information from a disk, when thedistance between the disk and focusing means is WDb.

FIG. 14A is a structural view of associated circuits of an optical headaccording to the first embodiment of the present invention.

FIG. 14B is a structural view according to a separate example ofassociated circuits of the optical head according to the firstembodiment of the present invention.

FIG. 15 is an outline of a signal that is output from the associatedcircuit of the optical head according to the first embodiment of thepresent invention.

FIG. 16A is a structural diagram of the manner in which a high densityoptical disk is recorded and reproduced in an optical system accordingto a second embodiment of the present invention.

FIG. 16B is a structural view of the manner in which a DVD is recordedand reproduced in an optical system according to the second embodimentof the present invention.

FIG. 17A is a view of an upper surface of a dichroic hologram that isused in the second embodiment of the present invention.

FIG. 17B is a view of a rear surface of a dichroic hologram that is usedin the second embodiment of the present invention.

FIG. 18A is a structural diagram of a separate example of the manner inwhich a high density optical disk is recorded and reproduced in theoptical system according to the second embodiment of the presentinvention.

FIG. 18B is a structural diagram of a separate example of the manner inwhich a DVD is recorded and reproduced in the optical system accordingto the second embodiment of the present invention.

FIG. 19A is a view of an upper surface of a separate example of adichroic hologram that is used in the second embodiment of the presentinvention.

FIG. 19B is a view of a rear surface of a separate example of a dichroichologram that is used in the second embodiment of the present invention.

FIG. 20A is a structural diagram of the manner in which a high densityoptical disk is recorded and reproduced in an optical system accordingto a third embodiment of the present invention.

FIG. 20B is a structural diagram of the manner in which a DVD isrecorded and reproduced in the optical system according to the thirdembodiment of the present invention.

FIG. 20C is a structural diagram of the manner in which a CD is recordedand reproduced in the optical system according to the third embodimentof the present invention.

FIG. 21A is a view of an upper surface of a dichroic hologram that isused in the third embodiment of the present invention.

FIG. 21B is a view of a rear surface of the dichroic hologram that isused in the third embodiment of the present invention.

FIG. 21C is a cross-sectional view of the dichroic hologram that is usedin the third embodiment of the present invention.

FIG. 22 is a cross-sectional view of the dichroic hologram according tothe third embodiment of the present invention.

FIG. 23A is a schematic view of a wavefront of the light of wavelengthλ2 after it has passed through the dichroic hologram used in the thirdembodiment of the present invention.

FIG. 23B is a schematic view of the wavefront of FIG. 23A that iscalculated ignoring the integer portion of the wavelength.

FIG. 24 is a conceptual diagram showing the diffraction efficiency oflight that is diffracted by the dichroic hologram used in the thirdembodiment of the present invention.

FIG. 25A is a schematic view of a wavefront of the light of wavelengthλ3 after it has passed through the dichroic hologram used in the thirdembodiment of the present invention.

FIG. 25B is a schematic view of the wavefront of FIG. 25A that iscalculated ignoring the integer portion of the wavelength.

FIG. 26 is a structural diagram of an optical head according to a fourthembodiment of the present invention.

FIG. 27A is a structural overview of an objective lens drive apparatusaccording to the fourth embodiment of the present invention.

FIG. 27B is a lateral view of the objective lens drive apparatusaccording to the fourth embodiment of the present invention.

FIG. 28 is an overview showing the structure of an optical headaccording to a fifth embodiment of the present invention.

FIG. 29A is a plan view of a phase plate according to the fifthembodiment of the present invention.

FIG. 29B is a lateral view of the phase plate according to the fifthembodiment of the present invention.

FIG. 30 is a diagram of wavefront aberration according to the fifthembodiment of the present invention.

FIG. 31 is a structural diagram of an optical head according to a sixthembodiment of the present invention.

FIG. 32A is a plan view of a phase plate according to the sixthembodiment of the present invention.

FIG. 32B is a lateral view of the phase plate according to the sixthembodiment of the present invention.

FIG. 33 is a diagram of the wavefront aberration according to the sixthembodiment of the present invention.

FIG. 34 is a structural diagram of an optical head according to aseventh embodiment of the present invention.

FIG. 35A is a plan view of a phase plate according to the seventhembodiment of the present invention.

FIG. 35B is a lateral view of the phase plate according to the seventhembodiment of the present invention.

FIG. 36 is a diagram of the wavefront aberration according to theseventh embodiment of the present invention.

FIG. 37 is a structural diagram of an optical head according to aneighth embodiment of the present invention.

FIG. 38 is a structural diagram of a mirror according to the eighthembodiment of the present invention.

FIG. 39A is a plan view of a phase plate according to a ninth embodimentof the present invention.

FIG. 39B is a lateral view of the phase plate according to the ninthembodiment of the present invention.

FIG. 40 is a structural diagram of an optical head according to a tenthembodiment of the present invention.

FIG. 41A is a plan view of a liquid crystal hologram according to thetenth embodiment of the present invention.

FIG. 41B is a lateral view of the liquid crystal hologram according tothe tenth embodiment of the present invention.

FIG. 42A is a plan view of a phase plate according to the tenthembodiment of the present invention.

FIG. 42B is a lateral view of the phase plate according to the tenthembodiment of the present invention.

FIG. 43 is a structural diagram of an optical head according to aneleventh embodiment of the present invention.

FIG. 44 is a structural diagram of an objective lens drive apparatusaccording to the eleventh embodiment of the present invention.

FIG. 45 is a diagram used to describe the manner in which the objectivelens is tilted.

FIG. 46 is a diagram used to describe positions of three spots accordingto the eleventh embodiment of the present invention.

FIG. 47 is a structural diagram of the optical head according to theeleventh embodiment of the present invention.

FIG. 48 is a structural diagram of an optical head according to atwelfth embodiment of the present invention.

FIG. 49A is a cross-sectional view of an objective lens according to thetwelfth embodiment of the present invention.

FIG. 49B is a view of a rear surface of the objective lens according tothe twelfth embodiment of the present invention.

FIG. 50 is a diagram used to describe tilt detection according to thetwelfth embodiment of the present invention.

FIG. 51 is a structural diagram of an optical head according to athirteenth embodiment of the present invention.

FIG. 52 is an overview of an optical disk drive that uses an opticalhead according to the present invention.

FIG. 53 is an external view of a personal computer that uses the opticaldisk drive of the present invention.

FIG. 54 is an external view of an optical disk recorder that uses theoptical disk drive of the present invention.

FIG. 55 is an external view of an optical disk player that uses theoptical disk drive of the present invention.

FIG. 56 is an external view of a server that uses the optical disk driveof the present invention.

FIG. 57 is a car navigation system that uses the optical disk drive ofthe present invention.

FIG. 58A is a structural diagram showing the manner in which a DVD isrecorded and reproduced by an optical head according to a firstconventional example.

FIG. 58B is a structural diagram showing the manner in which a CD isrecorded and reproduced by the optical head according to the firstconventional example.

FIG. 59 is a cross-sectional view of a dichroic hologram according tothe first conventional example.

FIG. 60A is a schematic view of a wavefront of the light of wavelengthλ2 after it has passed through the dichroic hologram used in the firstconventional example.

FIG. 60B is a schematic view of the wavefront of FIG. 60A that iscalculated ignoring the integer portion of the wavelength.

FIG. 61 is a structural diagram of an optical head according to a secondconventional example.

FIG. 62A is a plan view of a phase plate according to the secondconventional example.

FIG. 62B is a lateral view of the phase plate according to the secondconventional example.

FIG. 63 is a structural diagram of an objective lens according to athird conventional example.

FIG. 64 is a diagram that is used to explain the position of three spotsaccording to the third conventional example.

BEST MODE FOR CARRYING OUT THE INVENTION

According to a first optical element of the present invention, sincelight of a wavelength 380 to 420 nm can pass with favorable efficiency,and light of a wavelength 630 to 680 nm can be diffracted with favorableefficiency, a wavefront of light of different wavelengths can beconverted with little loss. Furthermore, manufacturing can besimplified, since it has two step grooves.

According to a second optical element of the present invention, sincelight of a wavelength 380 to 420 nm can pass with favorable efficiency,and light of a wavelength 630 to 680 nm can be diffracted with favorableefficiency, a wavefront of light of different wavelengths can beconverted with little loss. Furthermore, the efficiency of the lightthat is diffracted can be increased further, since it has four stepgrooves.

In the second optical element it is preferable that the depth of thegrooves is lined up in the order: depth 2 d, depth 4 d, depth d, depth 3d, or in the order: depth 3 d, depth d, depth 4 d, depth 2 d. Theefficiency of the light that is diffracted can be increased further inthis configuration.

Furthermore, it is preferable that the grooves are formed in concentricring-shapes. According to this configuration, light that has a flatwavefront that is incident on the optical element as collimated lightcan be converted to a converging wavefront or a diverging wavefront.Furthermore, it is also possible to add or remove spherical aberrationat the same time.

Furthermore, it is preferable that the grooves are adjacent via aportion in which no grooves are formed, and the width of each step ofthe grooves, is substantially the same as the width of the portion inwhich no grooves are formed. According to this configuration,manufacturing is simplified, and the efficiency of diffracted light canbe increased.

According to a first optical head of the present invention, a firstlight passes through the optical element with favorable efficiency andcan record onto and reproduce from the first optical information medium,and a second light is diffracted by the optical element with favorableefficiency and can record onto and reproduce from the second opticalinformation medium. Furthermore, manufacturing can be simplified, sinceit is a two step groove.

According to a second optical head of the present invention, the firstlight passes through the optical element with favorable efficiency andcan record onto and reproduce from the first optical information medium,and the second light is diffracted by the optical element with favorableefficiency and can record onto and reproduce from the second opticalinformation medium. Furthermore, the efficiency of the light that isdiffracted improves since the optical element has four step grooves.

In the first and the second optical heads, it is preferable that thedepth of the grooves is lined up in the order: depth 2 d, depth 4 d,depth d, depth 3 d, or in the order: depth 3 d, depth d, depth 4 d,depth 2 d. The efficiency of the light that is diffracted can beincreased further according to this configuration.

Furthermore, it is preferable that the second wavelength is 1.5 to 1.8times the length of the first wavelength. According to thisconfiguration, the efficiency of the light that is diffracted can beincreased further.

Furthermore, it is preferable that the grooves of the optical elementare formed on a face that is close to the focusing means. According tothis configuration, by bringing the focusing means closer to the groovesface of the optical element, manufacturing can be simplified becausegroove interval can be large even when making similar wavefront.

that contains the grooves, the efficiency of the light that isdiffracted can be further increased.

Furthermore, it is preferable that as for light of the second wavelengththat is diffracted by the optical element, the light that diverges isstronger than the light that converges with respect to incident light.According to this configuration, since the focal length of thediffracted light can be extended, the working distance can besubstantially fixed even when recording onto and reproducing from a diskwhose substrate thickness is thick.

Furthermore, it is preferable that the optical element corrects theaberration to not more than 70 mλ when light of the second wavelengththat is diffracted by the optical element is focused on an informationsurface of a second information recording medium. According to thisconfiguration, information can be recorded and reproduced reliably sincethe aberration of the diffracted light can be corrected to asufficiently small amount when information is recorded onto andreproduced from the second information recording medium.

According to a third optical head of the present invention, thestructure is simplified since a single optical element converts thewavefront of the second light and the third light, whose aberration wascorrected. Furthermore, since the third optical head is provided withgrooves whose depth is in two steps, through which the first lightpasses with favorable efficiency, and the second light is diffractedwith favorable efficiency, the wavefront of light of differentwavelength can be converted with less losses. Moreover, manufacturingcan be simplified, because it is a two step groove.

According to a fourth optical head of the present invention,manufacturing can be simplified because a single optical elementconverts the wavefronts of the second light and the third light, whoseaberrations were corrected. Furthermore, since the third optical head isprovided with grooves whose depth is in four steps, the wavelength oflight of different efficiencies can be converted with less loss becausethe first light passes with favorable efficiency, and the second lightis diffracted with favorable efficiency. Moreover, the utilizationefficiency of the light can be improved because it is a four stepgroove.

In a third and a fourth optical head, it is preferable that the depth ofthe grooves is lined up in the order: depth 2 d, depth 4 d, depth d,depth 3 d, or in the order depth 3 d, depth d, depth 4 d, depth 2 d.According to this configuration, the efficiency of the light that isdiffracted can be increased further.

Furthermore, it is preferable that the second wavelength is 1.5 to 1.8times the length of the first wavelength, and that the third wavelengthis 1.8 to 2.2 times the length of the first wavelength. According tothis configuration, the utilization efficiency of the light can beincreased further.

Furthermore, it is preferable that when a first region is asubstantially circle-shaped region in the central vicinity of the firstoptical element, a second region is a substantially ring-shaped regionthat surrounds the first region, and a third region is a region on theoutside of the second region,

-   -   light of the first wavelength passes through the first, second        and third region, light of the second wavelength passes through        the first and second region, and light of the third wavelength        passes through the first region. According to this        configuration, information can be reliably recorded and        reproduced because the light of each wavelength is converted        optimally wavefront using different regions of a single optical        element.

Furthermore, it is preferable that as for light of the second wavelengthand third wavelength that are diffracted by the first optical element,the light that diverges is stronger than the light that converges withrespect to incident light. According to this configuration, since thefocal length of the diffracted light can be extended, the workingdistance can be substantially fixed even when recording onto andreproducing from a disk whose substrate thickness is thick.

Furthermore, it is preferable that the third and fourth optical headsprovide phase correcting means for correcting the aberration of light ofthe second wavelength that is diffracted by the first optical element tonot more than 70 mλ when light of the second wavelength is focused onthe information surface of the second information recording medium, and

-   -   for correcting the aberration of light of the third wavelength        that is diffracted by the first optical element to not more than        70 mλ when light of the third wavelength is focused on the        information surface of the third information recording medium,    -   wherein the phase correcting means does not change the phase of        light of the first wavelength, and wherein the phase correcting        means is provided in the light path between the light sources        and the optical information recording medium. According to this        configuration, since aberration of the diffracted light can be        corrected to a sufficiently small amount during recording and        reproduction of the second information recording medium and the        third information recording medium, information can be recorded        and reproduced reliably.

Furthermore, it is preferable that a second optical element is furtherprovided that passes light of the first wavelength and light of thethird wavelength, and diffracts light of the second wavelength;

-   -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        two optical elements, after which they are focused by the        focusing means, and irradiated onto the optical information        recording medium. According to this configuration, the        aberration can be corrected to an even smaller amount and the        information can be reliably recorded and reproduced because two        optical elements are used for converting the wavefronts to        correct the aberration of the second light and of the third        light.

Furthermore, it is preferable that a second optical element is furtherprovided that passes light of the first wavelength and light of thethird wavelength, and diffracts light of the second wavelength;

-   -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        two optical elements, after which they are focused by the        focusing means, and irradiated onto the optical information        recording medium;    -   wherein the second optical element is an optical element in        which grooves are formed in a substrate;    -   wherein the expression:        760 nm≦(n1−1)×d≦840 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves; and    -   wherein the grooves are formed in two steps of depth d and depth        2 d. According to this configuration, the aberration can be        corrected to an even smaller amount and the information can be        recorded and reproduced reliably because two optical elements        are used to convert the wavefronts to correct the aberration of        the second light and of the third light. Moreover manufacturing        can be simplified, because it is a two step groove.

Furthermore, it is preferable that a second optical element is furtherprovided that passes light of the first wavelength and light of thethird wavelength, and diffracts light of the second wavelength;

-   -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        two optical elements, after which they are focused by the        focusing means, and irradiated onto the optical information        recording medium;    -   wherein the second optical element is an optical element in        which grooves are formed in a substrate;    -   wherein the expression:        760 nm≦(n−1)×d≦840 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves; and    -   wherein the grooves are formed in three steps of depth d, depth        2 d, depth 3 d. According to this configuration the aberration        can be corrected to an even smaller amount and the information        can be reliably recorded and reproduced because two optical        elements are used to convert the wavefronts to correct the        aberration of the second light and of the third light.        Furthermore, the utilization efficiency of the light can be        increased because the second optical element has three-step        grooves.

Furthermore, it is preferable that a second optical element is furtherprovided that passes light of the first wavelength and light of thethird wavelength, and diffracts light of the second wavelength,

-   -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        two optical elements, after which they are focused by the        focusing means, and irradiated onto the optical information        recording medium;    -   wherein the first optical element and the second optical element        are formed on a top and a rear of a single substrate. According        to this configuration, the single optical element can be        provided with two functions, so that the configuration of the        optical head is simplified.

Furthermore, it is preferable that a second optical element is furtherprovided that passes light of the first wavelength and light of thethird wavelength, and diffracts light of the second wavelength,

-   -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        two optical elements, after which they are focused by the        focusing means, and irradiated onto the optical information        recording medium; and    -   wherein the first optical element and the second optical element        are formed on a top and a rear of a single substrate, and the        face on which the second optical element is formed, of the two        faces of the single substrate, is closer to the focusing means.        According to this configuration, manufacturing is facilitated        because by causing the focusing means and a face of the grooves        of the second optical element to come closer, the groove        interval can be increased even when making similar wavefronts        for the second information recording media, which requires a        smaller groove interval.

Furthermore, it is preferable that a second optical element is furtherprovided that passes light of the first wavelength and light of thethird wavelength, and diffracts light of the second wavelength;

-   -   wherein light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        two optical elements, after which they are focused by the        focusing means, and irradiated onto the optical information        recording medium; and    -   wherein the first and second optical elements correct the        aberration of light of the second wavelength that is diffracted        by the first and the second optical elements to not more than 70        mλ when it is focused on the information surface of the second        information recording medium, and correct the aberration of        light of the third wavelength that is diffracted by the first        optical element to not more than 70 mλ when it is focused on the        information surface of the third information recording medium.        According to this configuration, information can be recorded and        reproduced reliably because the aberration can be corrected to a        sufficiently small amount when the diffracted light records onto        and reproduces from the second information recording medium and        the third information recording medium.

Furthermore, it is preferable that when a distance between the surfaceof the first information recording medium on the focusing means side,and the tip of the focusing means on the side of the first informationrecording medium is WD1 when light of the first wavelength is irradiatedonto the first information recording medium, and

-   -   a distance between the surface of the second information        recording medium on the focusing means side, and the tip of the        focusing means on the side of the second information recording        medium is WD2 when light of the second wavelength is irradiated        onto the second information recording medium, and    -   a distance between the surface of the third information        recording medium on the focusing means side, and the tip of the        focusing means on the side of the third information recording        medium is WD3 when light of the third wavelength is irradiated        onto the third information recording medium,    -   a difference between the maximum value and the minimum value of        WD1, WD2 and WD3 is smaller than the maximum value of the        diameter of the focusing means. According to this configuration,        the height of the focusing means can be stabilized further and        information can be recorded and reproduced with greater        reliability, even when recording and reproducing information on        different types of information recording media.

Furthermore, it is preferable that when a distance between the surfaceof the first information recording medium on the focusing means side,and the tip of the focusing means on the side of the first informationrecording medium is WD1 when light of the first wavelength is irradiatedonto the first information recording medium, and

-   -   a distance between the surface of the second information        recording medium on the focusing means side, and the tip of the        focusing means on the side of the second information recording        medium is WD2 when light of the second wavelength is irradiated        onto the second information recording medium, and    -   a distance between the surface of the third information        recording medium on the focusing means side, and the tip of the        focusing means on the side of the third information recording        medium is WD3 when light of the third wavelength is irradiated        onto the third information recording medium,    -   WD1, WD2 and WD3 are substantially equivalent. According to this        configuration, since the height of the focusing means is        substantially the same, the optical head can be small.

In any of the first to fourth optical heads, it is preferable that theyfurther a comprise converter for converting a plurality of signals,which are received in parallel and are output from the photodetectingmeans, into a serial signal. According to this configuration,fabrication of the optical head can be facilitated because the number ofsignal lines that link the optical head and the drive can be reduced.

It is also preferable that they further comprise a converter forconverting a plurality of signals, which are received in parallel andare output from the photodetecting means, into a serial signal, whereinthe serial signal is an electrical signal. According to thisconfiguration, the signal is easier to manage.

It is also preferable further to comprise a first converter forconverting a plurality of signals, which are output from thephotodetecting means and are received in parallel, into a serial signal;and a second converter for receiving the electric signal that is outputfrom the first converter and for converting the electric signal into anoptical signal. According to this configuration, there is nodeterioration of even a high frequency signal because the signal isconverted to an optical signal, and the signal can be output with lessnoise.

According to a first optical information recording and reproductionapparatus of the present invention, a first information recording mediumcan be recorded and reproduced by passing a first light through anoptical element with favorable efficiency, and a second informationrecording medium can be recorded and reproduced by diffracting a secondlight with favorable efficiency through the optical element.Furthermore, manufacturing can be simplified, since it has two stepgrooves.

According to a second optical information recording and reproductionapparatus of the present invention, a first information recording mediumcan be recorded and reproduced by passing a first light with favorableefficiency through an optical element, and a second informationrecording medium can be recorded and reproduced by diffracting a secondlight with favorable efficiency through the optical element.Furthermore, the efficiency of the diffracted light is further improvedbecause the optical element has four step grooves.

It is preferable that the second optical element of the second opticalrecording and reproduction apparatus of the present invention comprisesgrooves whose depth is lined up in the order: depth 2 d, depth 4 d,depth d, depth 3 d, or in the order depth 3 d, depth d, depth 4 d, depth2 d. According to this configuration, the efficiency of the diffractedlight can be further improved.

According to a third optical information recording and reproductionapparatus of the present invention, the structure is simplified becausea single optical element can convert the wavefront of a second light anda third light to correct aberration. Furthermore, since the thirdoptical information recording and reproduction apparatus providesgrooves that have a depth of two steps, and the first light passes withfavorable efficiency and the second light is diffracted with favorableefficiency, the wavefronts of light of different wavelength can beconverted with little loss. Moreover, manufacturing can be simplified,since it has two step grooves.

According to a fourth optical information recording and reproductionapparatus of the present invention, the structure is simplified becausea single optical element can convert the wavefront of a second light anda third light to correct aberration. Furthermore, since the fourthoptical information recording and reproduction apparatus providesgrooves that have a depth of four steps, and the first light passes withfavorable efficiency and the second light is diffracted with favorableefficiency, the wavefronts of light of different wavelength can beconverted with little loss. Moreover, the efficiency of the diffractedlight is further improved because the optical element has four stepgrooves.

In the third and fourth optical information recording and reproductionapparatuses of the present invention, it is preferable that a secondoptical element is further provided that passes light of the firstwavelength and light of the third wavelength, and diffracts light of thesecond wavelength, and that light of the first wavelength, light of thesecond wavelength and light of the third wavelength pass through the twooptical elements, after which they are focused by the focusing means andirradiated onto the optical information recording medium. According tothis configuration, the aberration can be corrected to an even smalleramount and the information can be recorded and reproduced reliablybecause two optical elements are used to convert the wavefronts tocorrect the aberration of the second light and of the third light.

According to a third optical element of the present invention, light,the wavelength 380 to 420 nm can be passed with favorable efficiency,and the wavefront of light of wavelength 630 to 680 nm can be converted.

In the third optical element of the present invention, it is preferablethat the steps are formed in a concentric ring-shapes. According to thisconfiguration, light that has a flat wavefront that is incident on theoptical element as collimated light can be converted to a convergingwavefront or a diverging wavefront. Furthermore, it is also possible toadd or remove spherical aberration at the same time.

According to a fifth optical head of the present invention, thewavelength 380 to 420 nm can be passed with favorable efficiency, andthe wavefront of light of wavelength 630 to 680 nm can be converted.

According to a sixth optical head of the present invention, loss oflight with respect to ultra high density optical disks (the firstinformation recording medium) and DVDs (the second information recordingmedium) can be suppressed using a simply constructed phase plate.

According to a seventh optical head of the present invention, generationof coma aberration can be decreased even when the focusing means ismoved in the tracking direction because the degree of divergence of thelight that is incident on the focusing means is small.

In any of the fifth to seventh optical heads, it is preferable furtherto provide tilting means for tilting the focusing means. In thisconfiguration, coma aberration can be cancelled out.

According to an eighth optical head of the present invention, a tiltingapparatus for the focusing means is not necessary because the light thatis incident on the focusing means is collimated light, and the opticalhead can be simplified.

In any of the fifth to eighth optical heads of the present invention, itis preferable that the optical element corrects the aberration of lightof the second wavelength when it is focused on the information recordingsurface of the second information recording medium to not more than 70mλ. According to this configuration, the wavefront aberration is lessthan the Marshall standard 70 mλ, the optical head has a diffractionlimit capability, and information can be recorded and reproducedfavorably.

According to a ninth optical head of the present invention, by providingan optical element that satisfies the expression, the wavefront of lightof the second wavelength can be converted without substantiallyaffecting the first light and the third light.

According to a tenth optical head of the present invention, by providinga liquid crystal element, if the liquid crystal element is in the OFFstate when the ultra high density optical disk (the first informationrecording medium) and the DVD (the second information recording medium)are used, then the light is not affected, and if the liquid crystalelement is in the ON state when the CD (the third information recordingmedium) is used, then the wavefront of the light can be converted.

According to an eleventh optical head of the present invention, a highdensity first information recording medium can be recorded andreproduced by a first light, a second information recording medium canbe recorded and reproduced by a second light, and a third informationrecording medium can be recorded and reproduced by a third light.Furthermore, the structure is simplified because a single opticalelement converts the wavefronts to correct the aberration of the secondlight and the third light.

In an eleventh optical head of the present invention, it is preferablethat a second optical element is further provided that passes light ofthe first wavelength and light of the third wavelength, and diffractslight of the second wavelength, and

-   -   that light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        two optical elements, after which they are focused by the        focusing means and irradiated onto the optical information        recording medium. According to this configuration, the        aberration can be corrected to an even smaller amount and the        information can be recorded and reproduced reliably because two        optical elements are used to convert the wavefronts to correct        the aberration of the second light and of the third light.

Furthermore, it is preferable that the second wavelength is 1.5 to 1.8times the length of the first wavelength, and that the third wavelengthis 1.8 to 2.2 times the length of the first wavelength. According tothis configuration, the light utilization ratio can be increasedfurther.

Furthermore, it is preferable that when a first region is asubstantially circle-shaped region in the central vicinity of the firstoptical element, a second region is a substantially ring-shaped regionthat surrounds the first region, and a third region is a region on theoutside of the second region,

-   -   light of the first wavelength passes through the first, second        and third region, light of the second wavelength passes through        the first and second region, and light of the third wavelength        passes through the first region. According to this        configuration, information can be recorded and reproduced        reliably because the light of each wavelength is converted        optimally wavefront using different regions of a single optical        element.

It is also preferable that as for light of the second wavelength andlight of the third wavelength that is diffracted by the optical element,the light that diverges is stronger than the light that converges withrespect to incident light. According to this configuration, since thefocal length of the diffracted light can be extended, the workingdistance can be substantially fixed even when recording onto andreproducing from a disk whose substrate thickness is thick.

It is also preferable that phase correcting means for correcting theaberration of light of the second wavelength that is diffracted by thefirst optical element to not more than 70 mλ when light of the secondwavelength is focused on the information surface of the secondinformation recording medium, and

-   -   for correcting the aberration of light of the third wavelength        that is diffracted by the first optical element to not more than        70 mλ when light of the third wavelength is focused on the        information surface of the third information recording medium,        is provided in the light path between the light sources and the        optical information recording medium, wherein the phase        correcting means does not change the phase of light of the first        wavelength. According to this configuration, information can be        recorded and reproduced reliably because diffracted light can        correct the aberration to a sufficiently small amount when        information is recorded and reproduced for the second        information recording medium and the third information.

It is also preferable that the second optical element is an opticalelement in which grooves are formed in a substrate;

-   -   wherein the expression:        760 nm≦(n−1)×d≦840 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves; and    -   wherein the grooves are formed in two steps of depth d and depth        2 d. According to this configuration, the aberration can be        corrected to an even smaller amount and the information can be        recorded and reproduced reliably because two optical elements        are used to convert the wavefronts to correct the aberration of        the second light and of the third light. Furthermore,        manufacturing can be simplified, since it has two step grooves.

It is also preferable that the second optical element is an opticalelement in which grooves are formed in a substrate;

-   -   wherein the expression:        760 nm≦(n−1)×d≦840 nm        is satisfied, where n is a refractive index of the substrate at        a wavelength of 400 nm, and d (nm) is a depth per step of the        grooves; and    -   wherein the grooves are formed in three steps of depth d, depth        2 d and depth 3 d. According to this configuration, the        aberration can be corrected to an even smaller amount and the        information can be recorded and reproduced reliably because two        optical elements are used to convert the wavefronts to correct        the aberration of the second light and of the third light.        Furthermore, the utilization efficiency of the light can be        increased because the second optical element has three step        grooves.

It is also preferable that the first optical element and the secondoptical element are formed on a top and a rear of a single substrate.According to this configuration, the single optical element can beprovided with two functions, so that the configuration of the opticalhead is simplified.

It is also preferable that the first optical element and the secondoptical element are formed on a top and a rear of a single substrate,and that the face on which the second optical element is formed, of thetwo faces of the single substrate, is closer to the focusing means.According to this configuration, manufacturing is facilitated because bycausing the focusing means and a face of the grooves of the secondoptical element to come closer, the groove interval can be increasedeven when making similar wavefronts for the second information recordingmedia, which requires a smaller groove interval.

It is also preferable that the first and second optical elements correctthe aberration of light of the second wavelength that is diffracted bythe first and the second optical elements to not more than 70 mλ when itis focused on the information surface of the second informationrecording medium, and correct the aberration of light of the thirdwavelength that is diffracted by the first optical element to not morethan 70 mλ when it is focused on the information surface of the thirdinformation recording medium. According to this configuration,information can be recorded and reproduced reliably because theaberration can be corrected to a sufficiently small amount when thediffracted light records onto and reproduces from the second informationrecording medium and the third information recording medium.

According to a twelfth optical head of the present invention, the heightof the focusing means can be stabilized further and information can berecorded and reproduced with greater reliability, even when recordingand reproducing information on different types of information recordingmedia.

According to a thirteenth optical head of the present invention, theheight of the focusing means is substantially the same, and informationcan be recorded and reproduced with greater reliability, even whenrecording and reproducing information on different types of informationrecording media.

According to a fourteenth optical head of the present invention,fabrication of the optical head can be facilitated because the number ofsignal lines that link the optical head and the drive can be reduced.

In the fourteenth optical head of the present invention, it ispreferable that the serial signal is an electrical signal. According tothis configuration, the signal is easier to manage.

Furthermore, it is preferable further to provide a second converter forreceiving the electric signal that is output from the first converterand for converting the electric signal into an optical signal. Accordingto this configuration, there is no deterioration of even a highfrequency signal because the signal is converted to an optical signal,and the signal can be output with less noise.

According to a fifth optical information recording and reproductionapparatus of the present invention, a high density first informationrecording medium can be recorded and reproduced by a first light, asecond information recording medium can be recorded and reproduced by asecond light, and a third information recording medium can be recordedand reproduced by a third light. Furthermore, the structure issimplified because a single optical element converts the wavefronts tocorrect the aberration of the second light and the third light.

In the fifth optical information recording and reproduction apparatus ofthe present invention, it is preferable that a second optical element isfurther provided that passes light of the first wavelength and light ofthe third wavelength, and diffracts light of the second wavelength, and

-   -   that light of the first wavelength, light of the second        wavelength and light of the third wavelength pass through the        two optical elements, after which they are focused by the        focusing means and irradiated onto the optical information        recording medium. According to this configuration, the        aberration can be corrected to an even smaller amount and the        information can be recorded and reproduced reliably because two        optical elements are used to convert the wavefronts to correct        the aberration of the second light and of the third light.

According to a fifteenth optical head of the present invention, sincethe outside diameter of a first focusing means is small, a secondoptical means also can move to the most inner circumference position,and is capable of reading in the information at the innermostcircumference position.

According to a sixteenth optical head of the present invention, tiltsensing can be performed using a simple configuration by utilizing lightof a wavelength that is not recording or reproducing information, suchthat it is not necessary to install a new tilt sensor, thus reducingcosts.

In the sixteenth optical head of the present invention, it is preferablethat the first focusing means emits light onto the information recordingmedium whose substrate thickness is 1.2 mm, and second focusing meansemits light onto the information recording media whose substratethickness is 0.1 mm and 0.6 mm.

It is also preferable that the first focusing means and the secondfocusing means are lined up in the tracking direction. According to thisconfiguration, it is possible to use the DPP method or the three beammethod, which are common tracking detection methods, and favorabletracking detection can be performed.

According to a seventeenth optical head of the present invention, thetilt control can be prevented from interfering with the focus control,since the information recording medium on which it is preferable toperform tilt adjustment, whose substrate thickness is thinnest, issubstantially in the center of a movable body.

In the seventeenth optical head of the present invention, it ispreferable to further provide tilting means that tilt the focusingmeans.

According to an eighteenth and a nineteenth optical head of the presentinvention, tilt sensing can be performed using a simple configuration byutilizing light of a wavelength that is not recording or reproducinginformation, such that it is not necessary to install a new tilt sensor,thus reducing costs.

In the eighteenth and nineteenth optical head of the present invention,it is preferable that the first wavelength is in the range 380 to 420nm.

Furthermore, in the nineteenth optical head, it is preferable that thefirst focusing means and the second focusing means are lined up in thetracking direction. According to this configuration, it is possible touse the DPP method or the three beam method, which are common trackingdetection methods, and favorable tracking detection can be performed.

It is also preferable that the second focusing means is provided with aregion through which light of a second wavelength passes without beingfocused. According to this configuration, the tilt of the firstinformation recording medium can be detected using the light that passesthrough this region.

It is also preferable that the second focusing means is provided with aregion through which light of the second wavelength is focused onto thefirst information recording medium. According to this configuration, thetilt of the first information recording medium can be detected using thelight that passes through this region.

It is also preferable that a holder on which the first focusing meansand the second focusing means is mounted, is provided with a throughhole through which light of the second wavelength passes. According tothis configuration, the tilt of the first information recording mediumcan be detected using light that passes through the hole in the holder.

According to a liquid crystal element of the present invention, it ispossible to change between a light influencing setting, and a setting inwhich the wavefront of the light is converted, depending on the type ofinformation recording media.

According to a computer, an image recording apparatus, a moving imagereproduction apparatus, a server and a car navigation system of thepresent invention, information can be recorded onto and reproduced fromdifferent types of optical disks reliably, and they can be used over awide range of applications.

Hereinafter, an embodiment of the present invention is described withreference to drawings. On each drawing given below, the same symbols aregiven to parts that perform the same action.

First Embodiment

FIG. 1 shows a structural view of an optical head 20 according to afirst embodiment of the present invention. The optical head 20 iscapable of at least either recording to or reproducing from (referred tobelow as “recording and reproduction”) an optical disk. FIG. 1A showsthe recording and reproduction state of a high density optical diskwhose substrate thickness is thin, FIG. 1B shows the recording andreproduction state of a DVD, and FIG. 1C shows the recording andreproduction state of a CD.

The optical head 20 is provided with three types of light source; a bluesemiconductor laser 21 (light source of a first wavelength) of awavelength of approximately 400 nm (380 nm to 420 nm), a redsemiconductor laser 22 (light source of a second wavelength) of awavelength of 630 nm to 680 nm, and an infrared semiconductor laser 23(light source of a third wavelength) of a wavelength of 780 nm to 820nm.

When recording and reproducing a high density optical disk 30 (FIG. 1A),light of a wavelength λ1 emitted from the blue semiconductor laser 21passes through wavelength selecting prisms 24 and 25, and is convertedto collimated light by a collimator lens 26. The light that was madeparallel is reflected by a beam splitter 27, passes through a dichroichologram (optical element) 28, is converted to convergent light by anobjective lens (focusing means) 29 and is irradiated onto the highdensity optical disk (a first information recording medium) 30.

The numerical aperture (NA) of the objective lens 29 is 0.85, and thesubstrate thickness of the high density optical disk is assumed to be0.1 mm. The objective lens 29 is designed such that the aberration is ata minimum, that is to say, such that the standard deviation of thewavefront aberration is at a minimum when the blue light of wavelengthλ1 is irradiated onto the disk of substrate thickness 0.1 mm.Furthermore, the dichroic hologram 28 is designed so as to allow thelight of wavelength λ1 to pass through it without being affected.

The light that was reflected by the high density optical disk 30,diffracted and modulated, passes again through the objective lens 29 andthe dichroic hologram 28, passes through the beam splitter 27, isconverted to convergent light by a detecting lens 31, and is incident ona photodetector (a photodetecting means) 32. The photodetector 32contains a plurality of photodetecting regions, and outputs a signal inresponse to the amount of light that is received.

When recording and reproducing a DVD 33 (a second information recordingmedium) (FIG. 1B), light of a wavelength λ2 emitted from the redsemiconductor laser 22 is reflected by the wavelength selecting prism24, passes through the wavelength selecting prism 25, and is convertedto collimated light by the collimator lens 26. The light that wasconverted to collimated light is reflected by the beam splitter 27, isdiffracted and wavefront converted by the dichroic hologram (opticalelement) 28, converted to converging light by the objective lens 29, andis irradiated onto the DVD 33.

The numerical aperture (NA) of the light emitted from the objective lens29 is limited to 0.6. The substrate thickness of the DVD 33 is 0.6 mm.The dichroic hologram 28 is designed such that when the red light ofwavelength λ2 irradiates the disk of the substrate thickness 0.6 mmafter passing through the objective lens 29, the standard deviation ofthe wavefront aberration is not more than 70 mλ.

The light that was reflected by the DVD 33, diffracted and modulated,passes again through the objective lens 29 and the dichroic hologram 28,passes through the beam splitter 27, is converted to converging light bythe detecting lens 31, and is incident on the photodetector 32. Thephotodetector 32 contains a plurality of photodetecting regions, andoutputs a signal in response to the amount of light that is received.

When recording and reproducing a CD 34 (third information recordingmedium) (FIG. 1C), light of a wavelength λ3 emitted from the infraredsemiconductor laser 23 is reflected by the wavelength selecting prism25, and is converted to collimated light by the collimator lens 26. Thelight that was converted to collimated light is reflected by the beamsplitter 27, is diffracted and wavefront converted by the dichroichologram (optical element) 28, is converted to converging light by theobjective lens 29, and is irradiated onto the CD 34.

The numerical aperture (NA) of the light emitted from the objective lens29 is limited to 0.4. The substrate thickness of the CD 34 is 1.2 mm.The dichroic hologram 28 is designed such that when the infrared lightof wavelength λ3 irradiates the disk of the substrate thickness 1.2 mmafter passing through the objective lens 29, the standard deviation ofthe wavefront aberration is not more than 70 mλ.

The light that was reflected by the CD 34, diffracted and modulated,passes again through the objective lens 29 and the dichroic hologram 28,passes through the beam splitter 27, is converted to converging light bythe detecting lens 31 and is incident on the photodetector 32. Thephotodetector 32 contains a plurality of photodetecting regions, andoutputs a signal in response to the amount of light that is received.

FIG. 2A shows an upper surface pattern of the dichroic hologram, andFIG. 2B shows a rear surface pattern. The light that approaches the diskenters from the rear surface (first optical element) 40 and exits froman upper surface (second optical element) 41. Light of wavelength λ3,which is in a range of 780 nm to 820 nm, is diffracted in a region 42 ofthe rear surface 40, and a pattern is formed so as to provide awavefront that is optimal to the CD 34 (such that the standard deviationof the wavefront aberration is not more than 70 mλ when focusing on theCD 34).

The light of wavelength λ3 passes through the upper surface 41 withoutbeing affected. Furthermore, the light of wavelength λ2, which is in arange of 630 to 680 nm, is diffracted by the pattern in the region 42 ofthe rear surface 40, after which it is also diffracted by the patternthat is formed in a region 43 on the upper surface 41.

The pattern within the region 43 is formed such that the light ofwavelength λ2 that was diffracted by both upper and rear surfaces has anoptimal wavelength for the DVD 33 (such that when focusing on DVD 33,the standard deviation of the wavefront aberration is not more than 70mλ). Because the principal object of the upper surface 41 and the rearsurface 40 is to apply power to the diffracted light and to correctspherical aberration, the pattern is concentric ring-shaped. Light inthe vicinity of wavelength λ1=400 nm passes through both upper and rearsurfaces without being affected.

FIG. 3 shows an enlarged cross-section of the rear surface 40 of thedichroic hologram 28. The rear surface 40 of the dichroic hologram isengraved with grooves that have four types of depth (d to 4 d). Thesegrooves are configured in a repeating pattern of a group of grooves thatare lined up as a single group in the order of 2 d, 4 d, d, 3 d andno-groove portion.

Here, depth d is:

-   -   d=λ1/(n1−1)        where n1 is the refractive index of a medium at the wavelength        λ1, which is selected from within the range 380 to 420 nm. The        phase shift in the light of wavelength λ1 that occurs due to the        light path difference between the indented groove portion and        the no-groove portion is an integer multiple of 2π by satisfying        this relationship. That is to say, the light path length        (n1−1)×d is equivalent to the wavelength λ1. Due to this, light        of the blue semiconductor laser of wavelength λ1 passes through        the dichroic hologram 28 unaffected (it is not diffracted).

If the wavelength is fixed, the light path length expressed by (n1−1)×dhas a unique value, and the effect that the light that is within thewavelength range 380 to 420 nm passes substantially through the dichroichologram 28 can be obtained if the light path length is within apredetermined range.

More specifically, it is preferable that the expression:380 nm≦(n1−1)×d≦420 nmis satisfied when the standard wavelength, from the range 380 to 420 nmof wavelengths of λ1, is 400 nm, and n is the refractive index of thesubstrate at a wavelength of 400 nm.

On the other hand, light of wavelength λ2 of the red semiconductor laserhas a modulated wavefront as shown in FIG. 4A. Because the light ofwavelength λ2 that records and reproduces DVDs is in the range 630 nm to680 nm, d is a depth that is equivalent to approximately 0.6 times thelength of wavelength λ2.

Consequently, 2 d is 1.2λ, 3 d is 1.8λ and 4 d corresponds to 2.4λ. Ifeach value is an integer multiple of λ then the phase shift of the lightdoes not occur, so that with regards to the phase of the light, integermultiples of λ can be ignored. Thus, considering only the fractionalparts smaller than the decimal point, d is 0.6λ, 2 d is 0.2λ (1.2λ−1λ),3 d is 0.8λ (1.8λ−1λ), and 4 d corresponds to 0.4λ (2.4λ−2λ).

Consequently the grooves arranged in the order of 2 d, 4 d, d and 3 dform wavefronts that have stepwise phase changes of 0.2λ, 0.4λ, 0.6λand0.8λ with respect to the light of wavelength λ2 as shown in FIG. 4B.That is to say that with respect to the light of wavelength λ2, thegrooves shown in FIG. 3 can be thought of as grooves that deepen in astepwise manner in the direction from the 2 d side to the 3 d side, asshown in FIG. 4B.

When grooves such as those shown in FIG. 3 are formed on the incidentface side (a boundary at which the light propagates from a medium of lowrefractive index (such as air) to a one of a high refractive index (suchas glass)) of an optical element, the intensity of light that isdiffracted in a direction 1 (the direction from the groove depth 3 dside toward the groove depth 2 d side) of FIG. 3 is stronger than lightthat is diffracted in a direction 2 (the direction from the groove depth2 d side toward the groove depth 3 d side).

Here, FIG. 5 shows the relationship between the groove depth of a singlestep that is standardized with respect to the wavelength λ, and anefficiency R, which is the efficiency of incident light that isconverted to first order diffracted light by a dichroic hologram such asthat whose cross-section is shown in FIG. 3. When the depth thatcorresponds to a single step is 0.6 times λ, the diffraction efficiencyis at its maximum, and it is possible to obtain a diffraction efficiencygreater than 0.8.

Furthermore, a wavefront of the light of wavelength λ3 of the infraredsemiconductor laser is modulated as shown in FIG. 6A. Because λ3 is in arange of 780 nm to 820 nm for the purpose of recording and reproducingCDs, d is a depth equivalent to approximately 0.5 times the length ofwavelength λ3.

Consequently, 2 d is 1.0λ, 3 d is 1.5λ and 4 d is equivalent to 2.0λ. Asdescribed previously, as the phase of the light, the integer multipleportions of λ can be ignored, so if only the portions smaller than thedecimal point are considered, then d is 0.5λ, 2 d is 0 (1.0λ−1λ), 3 d is0.5λ (1.5λ−1λ) and 4 d is equivalent to 0 (2.0λ−2λ). Consequently, thegrooves arranged in the order of 2 d, 4 d, d, 3 d form wavefronts thathave a two step phase of 0, 0, 0.5λ, 0.5λ, whose duty ratio is 3:2 withrespect to light of wavelength λ3 as shown in FIG. 6B. In this case,according to FIG. 5, a diffraction efficiency of about 0.3 can beobtained when the depth corresponding to a single step is 0.5 times λ.

FIG. 7 shows an enlarged cross-sectional view of the upper surface 41 ofthe dichroic hologram 28. The upper surface of the dichroic hologram 28is engraved with grooves of three different depths (d to 3 d). Thesegrooves are configured as a single group in a repeating pattern of agroup of grooves that are lined up in an order of d, 2 d, 3 d, andno-groove portion. Depth d is:

-   -   d=2×λ1/(n 1−1)        when n1 is the refractive index of a medium at a wavelength λ1,        which is selected from the range 380 to 420 nm. By satisfying        this relationship, the phase shift in the light of wavelength λ1        that occurs due to the light path difference between the        indented portion, which is the groove, and the no-groove portion        is an integer multiple of 2π. Due to this, light of the blue        semiconductor laser of wavelength λ1 passes through unaffected        by the dichroic hologram 28 (it is not diffracted).

In this case, the light path length, which is (n1−1)×d, is equivalent totwo times the wavelength λ1. As described previously, if the light pathlength is within a predetermined range then it is possible to achievethe effect that light of a wavelength, which is in a range of 380 to 420nm, can substantially pass through the dichroic hologram 28.

More specifically, it is preferable that the expression:760 nm≦(n1−1)×d≦840 nmis satisfied when the standard wavelength, from the range 380 to 420 nmof wavelengths of λ1, is 400 nm, and n is the refractive index of thesubstrate at a wavelength of 400 nm.

On the other hand, the light of wavelength λ2 of the red semiconductorlaser has a modulated wavefront as shown in FIG. 8A. Because the lightof wavelength λ2 that records and reproduces DVDs is in the range λ2=630nm to 680 nm, d is a depth that corresponds to approximately 1.2 timesthe length of wavelength λ2.

Consequently, 2 d is 2.4λ and 3 d is 3.6λ. As previously described,integer multiple portions of λ can be ignored for phases of the light,so if only the fractional parts smaller than the decimal point areconsidered, d is 0.2λ(1.2λ−λ), 2 d is 0.4λ (2.4λ−2λ) and 3 d is 0.6λ(3.6λ−3λ).

Consequently the grooves arranged in the order of d, 2 d, and 3 d formwavefronts that have stepwise phase changes of 0.2λ, 0.4λ, and 0.6λ withrespect to light of wavelength λ2 as shown in FIG. 8B. That is to saythat, with respect to the light of wavelength λ2, the grooves shown inFIG. 7 can be considered as grooves that deepen in a stepwise manner inthe direction from the d side to the 3 d side, as shown in FIG. 8B.

When grooves such as those shown in FIG. 7 are formed on the incidentface side of an optical element (a boundary at which the lightpropagates from one of a high refractive index (such as glass) to amedium of low refractive index (such as air)), the intensity of lightthat is diffracted in a direction 1 (the direction from the groove depth3 d side toward the groove depth d side) of FIG. 7 is stronger thanlight that is diffracted in a direction 2 (the direction from the groovedepth d side toward the groove depth 3 d side).

FIG. 9A shows the relationship between the groove depth of a single stepthat is standardized with respect to the wavelength λ, and an efficiencyR, which is the efficiency of incident light that is converted to firstorder diffracted light by a dichroic hologram 28 such as is shown inFIG. 7. When the depth corresponding to a single step is 1.2 times λ, adiffraction efficiency higher than 0.65 can be obtained.

Furthermore, the light of wavelength λ3 of the infrared semiconductorlaser has a wavefront that is modulated as shown in FIG. 8C. Because λ3is in a range of 780 nm to 820 nm for the purpose of recording andreproducing CDs, d is a depth equivalent to approximately 1.0 times thelength of wavelength λ3. Consequently, 2 d is 2.0λ and 3 d is equivalentto 3.0λ. As described previously, as the phase of the light, the integermultiple portions of λ can be ignored, so if only the portions smallerthan the decimal point are considered then all are equivalent to 0 asshown in FIG. 8 d. Consequently, the light of wavelength λ3 isunaffected by the dichroic hologram 28 (it is not diffracted), andsubstantially passes through it.

Here, FIG. 9B shows the relationship between the groove depth of asingle step that is standardized with respect to the wavelength λ, andan efficiency R, which is the efficiency of incident light that isconverted to zero order diffracted light by a dichroic hologram such asis shown in FIG. 7. When the depth corresponding to a single step is 1.0times λ, it is possible to obtain a transmittance of approximately 0.9.

In this way the light of wavelength λ1 at the rear surface (firstoptical element) 40 passes though the dichroic hologram 28 substantiallywithout being affected, while the light of wavelength λ2 and wavelengthλ3 are diffracted. Furthermore, at the upper surface (second opticalelement) 41, the light of wavelength λ1 and λ3 pass through and thelight of wavelength λ2 is diffracted.

Due to this, information can be recorded and reproduced reliably becauselight sources that have appropriate wavelengths for each of the threetypes of optical disks (information recording media) are used and lightof low aberration can be focused on the information surface withexcellent efficiency. Furthermore, the same effect also can be obtainedwhen there are two types of optical disk.

It should be noted that the dichroic hologram 28 used here has the firstoptical element and the second optical element formed on the uppersurface 41 and the rear surface 40 as a single piece. However it is alsopossible to arrange a dichroic hologram such that the first opticalelement and the second optical element are formed on separate elements.In that case, their centers can be matched up to the optical axis byadjusting the position of both optical elements.

Furthermore, it is preferable that the dichroic hologram 28 isfabricated from glass. If it is fabricated from resin, then it ispreferable to use amorphous polyolefin based resins whose absorbtance isnot more than 5%, and whose absorptance is preferably not more than 3%.This is due to the fact that light of a wavelength of not more than 420nm has a strong chemical action, so there is a possibility that theresin may be damaged if an optical element of high absorptance isirradiated over a long period. It is relatively difficult to damageamorphous polyolefin based resins, even by irradiating with light of awavelength less than 420 nm.

Moreover, it is also possible to fabricate one of the optical elementson the surface of the objective lens. In this case, it is possible toincrease the positional accuracy of the optical axis of the objectivelens.

Furthermore, the diffraction efficiency shown here is a value that iscalculated when the widths of adjacent grooves of different depths aresubstantially equivalent.

Furthermore, even if the grooves are lined up in a sequence that iscompletely opposite to the examples given here, the same effect can beobtained apart from a change in the direction in which the light isefficiently diffracted.

Furthermore, it goes without saying that even if the start point of theway the grooves are lined up, and the way the grooves are described ischanged, if the grooves are actually lined up in the same sequence, thenthe same effect can be obtained.

Moreover, the wavelengths λ1 and λ2 satisfy the relationship1.5≦λ2/λ1≦1.8,and the wavelengths λ1 and λ3 satisfy the relationship1.8≦λ3/λ1≦2.2.

Furthermore, as shown in FIG. 10, the light of wavelength λ2, which isdiffracted by the dichroic hologram 28 is designed such that thediffraction efficiency of the light of wavelength λ2 that is diffractedfrom collimated light to diverging light (direction 1) by the dichroichologram 28, is greater than the diffraction efficiency on the side inwhich it is diffracted to converging light (direction 2). Morespecifically, grooves such as are shown in FIG. 3 are arranged in aconcentric ring shape on the incident face such that the direction 1approaches the circumference, and the direction 2 approaches the center,and moreover, on the exit face side, grooves such as are shown in FIG. 7are arranged in a concentric ring-shape such that the direction 1approaches the circumference, and the direction 2 approaches the center.In this way, because the diffraction efficiency in the direction 1 ishigher than the diffraction efficiency in the direction 2, thediffracted light is substantially converted to diverging light, and thedichroic hologram 28 acts as a concave lens.

Thus, a focal length f of the focusing optical system, which is matchedto the objective lens, lengthens and even DVDs, which at 0.6 have athicker substrate than a substrate thickness of 0.1, can be operated ata relatively large working distance.

It should be noted that there is no particular discussion here ofmethods for limiting the aperture of the light of wavelength λ2 or thelight of wavelength λ3, however there is the method of vapor depositinga wavelength selecting filter onto the dichroic hologram 28 or theobjective lens 29, or the method of providing a separate glass filter.Furthermore, it is also possible to control the aperture by providing anopening across the light path that is passed only by light of a singlewavelength (in the region between the light source and the wavelengthselecting prism).

FIG. 11 shows an entire structural example of an optical disk drive 50as an optical information recording and reproduction apparatus. Anoptical disk 51 is fixed by sandwiching between a turntable 52 and adamper 53, and is rotated by a motor (rotating system) 54, which is amoving means. An optical head 20 is mounted on a traverse (conveyingsystem) 55, which is a moving means, and the point that is irradiated bylight is capable of moving from the inner circumference of the opticaldisk 51 to the outer circumference. The control circuits 56 performfocus control, tracking control, traverse control and rotational controlof the motor and the like based on signals received from the opticalhead 20.

FIG. 12 shows the working distance when recording and reproducing eachdisk. The height of the side at which light is incident on the opticaldisk is determined by the position of the turntable 52. On the otherhand, the relative height of fixing elements 60 on the actuator of theoptical head 20 with respect to the turntable 52 is determined uniquelyby the structure and the positional relationship of the traverse 55 andthe motor 54. Furthermore, the position of a movable element 61 of theactuator that moves the objective lens 29 in the focus direction isdetermined by the position of the recording surface of the optical disk,and by back focus on the disk side of the objective lens 29, which isthe focusing means. Back focus means the length between the tip of thefocusing means to the point of convergence of the light rays. The tip ofthe focusing means more specifically that, of the intersections betweenthe objective lens 29 and the optical axis, it is the intersection thatis on the optical disk side.

The working distance WD isWD=BF−t/nwhen the refractive index at the wavelength λ is n, the substratethickness of the disk is t and the back focus is BF. For example, on adisk in which the substrate thickness is thick, and t/n is large, theworking distance WD becomes small such that if the focusing means notdesigned such that the back focus BF can change in response to thatchange, then the working distance WD will vary greatly when there is achange in substrate thickness.

FIG. 12 shows the working distance WD at a working distance WD1 (FIG.12A), a working distance WD2 (FIG. 12B) and a working distance WD3 (FIG.12C), depending on the type of optical disk, that is, depending onchanges in the substrate thickness.

A configuration according to a conventional example is shown in FIG. 13,showing the case in which a working distance changes greatly dependingon the type of optical disk. When there is a large change in workingdistance due to the type of the optical disk, there is a large change inthe relative distance between the fixing elements 60 of the actuator andthe movable element 61.

Because a working distance WDa in FIG. 13A is small, the movable element61 is relatively higher than the upper side (disk side) of the fixingelements 60. However as in FIG. 13B, when the working distance WDb islarge, the moving element 61 is relatively lower than the lower side(side furthest from the disk) of the fixing elements 60. Because regularoptical disks droop on their inner and outer circumferential sides andhave shake of disc in focusing direction when rotating, to a certainextent the fixing elements 60 cover the vertical movement range of themovable element 61. However, when there is a difference in workingdistance, there is a problem in that to absorb that difference, the sizeof the actuator increases, and the overall size of the optical head.increases. Furthermore, when the movable range is large, the movableelement 61 tilts depending on the position of the movable element 61,and there is the problem that the optical system is susceptible togenerating aberrations.

The moveable range of the moveable element 61 also depends on thestructure of the actuator, however it is preferable that it is less thanthe lateral direction width of the moveable element 61. This is because,if the lateral width is large, even if a height difference developsbetween left and right, then the tilting angle is small. However, if thelateral width is small, even with a minimal left and right heightdifference, the tilting angle becomes large.

Consequently, the difference in working distance caused by disk type,that is to say, the movable range of the movable element 61 ispreferably smaller than the lateral width of the movable element 61. Inthe example of FIG. 12, it is preferable that the maximum and minimumdifferences between WD1, WD2 and WD3, being the difference in workingdistance caused by disk type, are smaller than the lateral width of themovable element 61.

In the case of the ultra high density optical disk, when NA=0.85, andthe focal length f of the focusing means is 2.0 mm, the beam diameter isφ3.4 mm. Because the minimum value of the width of the movable element61 is this beam width, in this case there is a need to set thedifference between the maximum value and minimum value of the workingdistance to 3.4 mm at most.

It should be noted that when considering the actual size of theactuator, the movement range of the actuator is at best 1 mm, so that itis preferable that the difference between the maximum working distanceand minimum working distance is not more than half that at 0.5 mm.Moreover, in order not to substantially affect the size of the actuator,it is preferable that the difference between the maximum value and theminimum value of the working distance is not more than 0.2 mm. Ofcourse, the most preferable state is the one in which the workingdistance is equivalent when recording onto and reproducing informationfrom differing types of information recording media, and in which thedifference between the maximum value and the minimum value is 0.

In the present embodiment, since the back focus BF can be set optimallyusing the dichroic hologram 28 according to the disk that is recorded orreproduced, the WD can be substantially fixed during recording andreproduction of each disk.

More specifically, in the example given previously, light from the bluesemiconductor laser (wavelength λ1) is not diffracted by the dichroichologram 28, and the diffraction efficiency of the light from the redsemiconductor laser (wavelength λ2) is set to differ from thediffraction efficiency of the light from the infrared semiconductorlaser (wavelength λ3). Thus, light of the blue semiconductor laserpasses as is through the dichroic hologram 28, the degree of divergenceof the light of the red semiconductor laser differs from the degree ofdivergence of the light of the infrared semiconductor laser, and it ispossible to change the back focus depending on the light from eachlaser. That is to say, it is possible to design the dichroic hologram 28so as to control the back focus depending on the type of disk, and it ispossible to substantially fix the WD without consideration to the typeof disk.

If the WD can be substantially fixed in this way, then the size of theentire optical head can be reduced, and because the movable range of themovable element 61 can be reduced, it is possible to suppress thegeneration of aberrations caused by tilt of the movable element 61.

FIG. 14 shows an example that unifies the signal output from the opticalhead of the present embodiment. An optical head 70 has the same opticalstructural elements as the optical head 20. It differs in the provisionof a P/S (parallel/serial) converting circuit 71 (parallel/serialconverter) that converts the output signal from the photodetector 32that is received as a parallel signal into a serial signal. A P/Sconverting circuit 71 receives signals through a plurality of signallines from the photodetector 32, time divides and lines them upserially, and outputs them as an output signal through a single signalline.

As a method for this, there is the method of sequentially switching ananalog switch in an internal portion of the P/S converting circuit basedon the clock, which is a timing signal, and outputting the serial signalas an output signal. Furthermore, a method is also possible in which thesignal that is obtained in parallel is subjected to analog/digitalconversion (A/D conversion), stored in memory and then transmitted asdigital data in a serial sequence. FIG. 15 shows an example of thesignal in such a case. Synchronised with the clock as the timing signal,digital signals such as an RF signal, and FE+ signal, an FE− signal, aTE+ signal and a TE− signal and the like are transmitted.

Thus, the number of signal lines between the optical head and thecontrol circuits and the like of the optical disk drive can be reduced.In optical heads that record and reproduce CDs and DVDs as well as highdensity optical disks, approximately three times the usual amount ofsignal lines are necessary just to drive the semiconductor lasers, whichare the light source. FIG. 14A shows an example in which thephotodetector (photodetecting means) is shared, and as shown in FIG.14B, also conceivable is a case in which the photodetector(photodetecting means) is not shared, and which has the photodetector(photodetecting means) 72 and a photodetector (photodetecting means) 73,and a case which contains three photodetectors. In these cases, there isa further increase in signal lines, the width of the flexible cable thatconnects the optical head and the drive is enlarged, and there is theproblem of a loss of flexibility (the ease of bending) of the flexiblecable. Furthermore, if the flexible cable is changed to a multilayerflexible circuit, then although the width of the flexible cable can bereduced, there is the problem of an increase in cost.

If the optical head is an optical head 75 that is provided with a P/Sconverting circuit 74 for receiving signals in parallel from thephotodetector 72 and the photodetector 73, and outputting them as serialsignals such as is shown in FIG. 14B, then the number of signal linescan be greatly reduced.

In the example of the optical head 75 in FIG. 14B, the signal from theP/S converting circuit 74 is converted to an optical signal by an LED(electrical/optical converter) 76 and is output to an optic fiber 77. Inthis case, it is possible to transmit a higher frequency signal than anelectric signal yet with lower noise, and there is the advantage thatthese signals can be transmitted with sufficient accuracy and period oftime even if there is an increase in the number of signals to beconverted.

It should be noted that the example in which the P/S converting circuitis utilized is not limited to optical heads in which light sources ofthree wavelengths are used, and the same effect can be obtained withoptical heads containing light sources of one wavelength or twowavelengths. In these cases as well, if a plurality of signal lines areneeded for tracking signals or focus signals, then the optical head canbe consolidated into a single unit. Furthermore, if A/D conversion isperformed within the optical head, then because paths that introducenoise can be shortened, this is also effective in raising the SN ratioof the signal.

Second Embodiment

An example of an optical head applied interchangeably to high densityoptical disks and DVDs is described as a second embodiment. FIG. 16 is astructural example of an optical head 80. As shown in FIG. 16A, a lightof wavelength λ1 emitted from a blue semiconductor laser (a light sourceof a first wavelength) 21 passes through the wavelength selecting prism24, and is converted to collimated light by the collimator lens 26. Thelight that was converted to collimated light is reflected by the beamsplitter 27, passes through the dichroic hologram (optical element) 81,is focused by the objective lens (focusing means) 29 and is irradiatedonto the high density optical disk (first information recording medium)30.

The numerical aperture (NA) of the objective lens is 0.85, and thesubstrate thickness of the high density optical disk 30 is assumed to be0.1 mm. The objective lens 29 is designed such that spherical aberrationis at a minimum when the blue light of wavelength λ1 is radiated onto adisk whose substrate thickness is 0.1 mm.

Furthermore, the dichroic hologram 81 is designed so as to pass thelight of wavelength λ1 without affecting it. The light that wasreflected by the high density optical disk 30, diffracted and modified,again passes through the objective lens 29 and the dichroic hologram 81,passes through the beam splitter 27, is focused by the detecting lensand is incident on a photodetector (photodetecting means) 82. Thephotodetector 82 contains a plurality of photodetecting regions, andoutputs a signal in response to the amount of light that is received.

As shown in FIG. 16B, when recording and reproducing the DVD 33 (secondinformation recording medium), the light of wavelength λ2 is emittedfrom the red semiconductor laser 22, is reflected by the wavelengthselecting prism 24 and is converted to collimated light by thecollimator lens 26. The light that was converted to collimated light isreflected by the beam splitter 27, is diffracted by the dichroichologram 81 and wavefront converted, is focused by the objective lens 29and is irradiated onto the DVD 33.

Here, the numerical aperture (NA) of the light that is emitted from theobjective lens is limited to 0.6. The substrate thickness of the DVD 33is 0.6 mm. The dichroic hologram 81 is designed such that when the redlight of wavelength λ2 that has passed through the objective lens 29 isirradiated on to the disk of substrate thickness of 0.6 mm, the standarddeviation of wavefront aberration is not more than 70 mλ.

The light that was reflected at the DVD 33, diffracted and modulated,again passes through the objective lens 29 and the dichroic hologram 81,passes through the beam splitter 27, is focused by the detecting lens31, and is incident on the photodetector 82. The photodetector 82contains a plurality of photodetecting regions, and outputs a signal inresponse to the amount of light that is received.

FIG. 17 shows a pattern on the upper surface (the disk side) and therear side (the side that is furthest from the disk) of the dichroichologram 81. The light that approaches the disk passes through from therear surface to the upper surface. No particular pattern is formed onthe rear surface shown in FIG. 17B. On the upper surface that is shownin FIG. 17A, the light in the range of wavelength λ2=630 to 680 nm isdiffracted by a pattern within a region 83.

The pattern within the region 83 is formed such that the light ofwavelength λ2 that was diffracted at the upper surface has a wavefrontthat is optimal for the DVD 33. Since the principal object is to applypower to the diffracted light and to correct spherical aberration, thepattern is concentric ring-shaped. Light in the vicinity of wavelengthλ1=400 nm passes through both upper and lower surfaces without beingaffected.

The cross-sectional form of the hologram that is formed on the uppersurface of the dichroic hologram 81 is the same as the cross-sectionalform of that which is formed on the rear surface 40 of the dichroichologram 28 of the first embodiment. Accordingly, because highdiffraction efficiencies can be obtained for the light of wavelength λ2that is in the range 630 to 680 nm, satisfactory light utilizationefficiency can be achieved.

Consequently, since it is possible to use light sources whose respectivewavelengths are appropriate to the types of optical disks (informationrecording media), namely high density optical disks 30 and DVDs 33, andto focus light with less aberrations onto the information surfaces athigh efficiencies, information can be recorded and reproduced reliably.

As in the present embodiment, by setting the surface of the dichroichologram 81 on which the pattern is provided to be the face closest tothe objective lens, it is possible to prevent the minimum pitch of thedichroic hologram 81 from becoming too small, thus facilitatingfabrication of the dichroic hologram 81.

Furthermore, because recording and reproduction of CDs is omitted fromthe present embodiment, not only is a light source for CDs unnecessary,but the shape of the dichroic hologram 81 is simplified, and since thevariety of signals that the photodetector 82 detects is reduced, thephotodetector is simpler than that of the first embodiment.

Furthermore, FIG. 18 shows an optical head 84 that uses a dichroichologram 85 in place of the dichroic hologram 81. FIG. 18A is astructural overview of the high density optical disk 30 during recordingand reproduction, and FIG. 18B is a structural overview of the DVD 33during recording and reproduction. FIG. 19 shows a pattern on an uppersurface (disk side) and rear surface (side furthest from the disk) ofthe dichroic hologram 85. The upper surface of the dichroic hologram 85that is shown in FIG. 19A has the same pattern that is formed on theupper surface of the dichroic hologram 81 shown in FIG. 17. A pattern,which is a hologram for correcting chromatic aberration in light ofwavelength λ1, is formed in a region 87 on the rear surface of thedichroic hologram 85 shown in FIG. 19B.

Holograms for correcting chromatic aberrations are explained in detailin the Patent Document 3 (JP 2001-60336A). In this specification, thecross-section of the optical element is saw tooth-shaped, and a methodis described whereby second order diffracted light is used forcorrecting light of a first wavelength λ1, and first order diffractedlight is used for correcting light of a second wavelength λ2. Aberrationthat occurs at the objective lens caused by wavelength offset of thelight of wavelength λ1 is cancelled out by changes in the diffractingangle of the diffraction grating to correct chromatic aberration.Accordingly chromatic aberration can be corrected without the additionof new parts.

Furthermore, an example of an optical head is described in the presentembodiment. However, as in the structure in FIG. 11 of the firstembodiment, by providing moving means such as a conveying system 55 or arotating system 54, and a control circuit 56, the optical head can beused as an optical information recording and reproduction apparatus(optical disk drive).

Third Embodiment

A third embodiment shows an example of a head that records andreproduces information onto three types of optical disks using threetypes of light sources using an optical element that has a dichroichologram on one face and a phase shift step on an opposite face.Furthermore, a dichroic hologram that has two types of groove depths isdescribed.

FIG. 20 is a structural overview of an optical head 90 according to thepresent embodiment. Parts that are the same as in the first and secondembodiment are given the same symbols, and the description thereof ishereby omitted. The present embodiment differs from the first and secondembodiments in the use of a dichroic hologram (optical element) 91,which has a phase shift step on its rear surface.

A front view of the dichroic hologram 91 is shown in FIG. 21, while FIG.21A shows an upper surface (disk side), FIG. 21B shows a rear surface(side furthest from the disk), and FIG. 21C is a cross-sectional view ofFIG. 21B. As shown in FIG. 21A, grooves are formed as a dichroichologram in a circle-shaped region 93 (first region) in the vicinity ofthe center of an upper surface 92, and in a ring-shaped region 94(second region) that wraps around the region 93. No grooves are formedin a region 95 (third region) that is on the outer side of the region94.

On the other hand, as shown in FIG. 21B, a phase shift step (phasecorrecting means) 97 is formed on a rear surface 96. The light ofwavelength λ1=380 nm to 420 nm passes as is through the dichroichologram on the upper surface, but the light of wavelength λ2=630 nm to680 nm and the light of wavelength λ3=780 nm to 820 nm is diffracted.The light of wavelength λ1 passes through the region 93 and the region94 and one part of the region 95.

The light of wavelength λ3 that reproduces the CD 34 passes through therear surface 96, after which it irradiates only onto the region 93 ofthe upper surface 92. The pattern of the region 93 is designed such thatwhen the light of wavelength λ3 that was diffracted is irradiated ontothe CD 12 of t=1.2 mm, the standard deviation of the wavefrontaberration is not more than 70 mλ.

The phase shift step 97 of the rear surface 96 shown in FIG. 21B is astep that does not affect the light of wavelength λ1 and the light ofwavelength λ3. The light of wavelength λ2 is phase modulated by thephase shift step 97 of the rear surface 96, and is irradiated onto thecircle-shaped region 93 (first region) and the ring-shaped region 94(second region) of the upper surface 92.

The shape of the pattern in the ring-shaped region 94 and the phaseshift step 97 (phase correcting means) is designed such that thestandard deviation of the wavefront aberration is not more than 70 mλwhen the light that was diffracted at the circle-shaped region 93 andthe ring-shaped region 94 is irradiated onto the DVD 33 of t=0.6.

FIG. 22 shows an enlarged cross-sectional view of the dichroic hologram91. The surface of the dichroic hologram 91 is engraved with groovesthat have two types of depths (d and 2 d). Those grooves form sets ofgrooves lined up in the order d, 2 d, no groove, and are formed as arepetition of those sets. Where a refractive index of a medium atwavelength λ1 that is within the range of 380 nm to 420 nm is n1, thedepth d is expressed by:d=λ1/(n1−1).Accordingly, the light of wavelength λ1 from the blue lightsemiconductor laser passes through without any effect.

Furthermore, as described in the first embodiment, if the light pathlength is within a predetermined range, then the effect that lightwithin the wavelength range 380 nm to 420 nm substantially passesthrough the dichroic hologram can be obtained. Thus, it is preferablethat the expression:380 nm≦(n−1)×d≦420 nmis satisfied, where n is the refractive index of the substrate at awavelength of 400.

On the other hand, the wavefront of the light of wavelength λ2 of thered semiconductor laser is modulated as shown in FIG. 23A. Since thewavelength λ2 is in the range 630 nm to 680 nm for recording andreproduction of the DVD 33, d has a depth that corresponds toapproximately 0.6 times the length of the wavelength λ2. Consequently, 2d corresponds to 1.2λ. Since the integer multiples of λ can be ignoredin the phases of light, with consideration given only to the portion onthe right of the decimal point, d corresponds to 0.6λ and 2 dcorresponds to 0.2λ. Consequently, grooves that are lined up in theorder d, 2 d form wavefronts having phases that change stepwise as 0.6λand 0.2λ, as shown in FIG. 23B.

FIG. 24 shows the relationship between a groove depth of a single stepthat is normalized by the wavelength λ, and the efficiency R ofconverting incident light to first order diffracted light at thedichroic hologram, such as is shown in FIG. 22. From FIG. 24, adiffraction efficiency in the order of 0.6 can be obtained when thedepth of one step is 0.6 times λ.

Furthermore, the wavefront of the light of wavelength λ3 of the infraredsemiconductor laser is modulated as shown in FIG. 25A. Since thewavelength λ3 is in the range 780 nm to 820 nm for CD recording andreproduction, d has a depth that corresponds to approximately 0.5 timesthe length of wavelength λ3. Consequently, 2 d corresponds to 1.0λ.Since the integer portions of λ can be ignored in the phases of light,with consideration given only to the part to the right of the decimalpoint, d corresponds to 0.5λ and 2 d corresponds to 0.

Consequently, grooves that are lined up in the order d, 2 d, formwavefronts having two step phases are 0.5λ and 0 as shown in FIG. 25B,whose duty ratio is 1:2. Due to this, a diffraction ratio in the orderof 0.3 can be obtained when the depth of one step is 0.5 times λ, asshown in FIG. 24.

If the dichroic hologram 91 as shown in FIG. 21 is used, then thehologram pattern is only fabricated on one face, and since the rearsurface is constituted by a phase shift step that has lowlight-intensity-loss, light utilization efficiency can be raised.

Thus, since it is possible to use light sources having wavelengths thatare appropriate to the three types of optical disks (informationrecording media) to focus low aberration light onto the informationsurface at high efficiency, information can be recorded and reproducedreliably.

It should be noted that here, the dichroic hologram and the phase shiftstep are formed on the upper surface and rear surface of a singleoptical element. However it is also possible to arrange a member inwhich these are formed on separate optical elements. In this case, bytuning the position of both optical elements, it is possible to adjusttheir centers to the optical axis.

Furthermore, the diffraction efficiency shown here is a value calculatedwhen the width of adjacent grooves of various depths is substantiallyequivalent.

Moreover, the relationship between the wavelengths λ1 and λ2 satisfies:1.5≦λ2/λ1≦1.8,and the relationship between the wavelengths λ1 and λ3 satisfies:1.8≦λ3/λ1≦2.2.

The conventional example disclosed in Patent Document 1 (JP H9-306018A),is illustrated by an example that has three types of groove depths,which allows one wavelength to pass through and diffracts anotherwavelength. However, there is no mention of the fact that when thewavelengths of λ1 and λ2 have the relationship:1.5≦λ2/λ1≦1.8,a dichroic hologram that has two types of groove depths, or a dichroichologram that has four types of groove depths in which these groovedepths are lined up in the order 2 d, 4 d, d, 3 d, no groove, canincrease the diffraction efficiency of light of wavelength λ2. This issubject matter that is first disclosed by the present invention.Furthermore, the fact that an appropriate diffraction ratio of light ofthe wavelength λ3 that has the relationship:1.8≦λ3/λ1≦2.2.can be obtained with the aforementioned dichroic hologram is anotheroriginal disclose of the present invention.

It should be noted that it is also possible that the hologram that isgrouped with the phase shift step is of the shape that has four types ofgroove depths that are shown in the first embodiment. Similarly, it isalso possible to use a dichroic hologram of a form having two types ofgroove depths, as shown in the third embodiment, applied to the dichroichologram of the first embodiment.

It should be noted that for simplicity, the light sources here areseparate, and the photodetector is shared, however a single light sourcesuch as a monolithic semiconductor laser also can be used as thelightsource, and the photodetectors also can be separate. Even with thisconfiguration, the same effect can be demonstrated.

Furthermore, a disk whose substrate thickness t=0.1 and numericalaperture is 0.8 has been assumed as the example of the high densityoptical disk. However it is not limited to this.

Also, although the present embodiment has been described using theexample of an optical head, by providing a moving means such as thetraverse system 55 or the rotating system 54, and the control circuit56, it can be used as the optical information recording and reproductionapparatus (optical disk drive), as shown in FIG. 11 of the firstembodiment.

Fourth Embodiment

FIG. 26 shows a structural view of the optical head according to afourth embodiment of the present invention. It differs from the opticalhead according to the second conventional example in that it is providedwith an objective lens drive apparatus 44 that is capable of tilting theobjective lens 11. FIG. 26 shows the manner in which an ultra highdensity optical disk 12, which has a substrate thickness of 0.1 mm andan optical disk (DVD) 13, which has a substrate thickness of 0.6 mm, arerecorded and reproduced. In order to simplify the description, bothdisks are drawn overlapped in the same location.

The optical head shown in this drawing is provided with a light source 1that produces a wavelength 380 nm to 420 nm (wavelength λ1), and amodule 2 a. A photodetector and a light source of light of a wavelength630 nm to 680 nm (wavelength λ2) are contained within the module 2 a.During recording and reproduction of the ultra high density optical disk12, the light of wavelength λ1 that is emitted from the light source 1passes through prisms 4 and 6 and is converted to collimated light by afocusing lens 7. This collimated light is reflected by a mirror 8,passes through a phase plate 9, is focused by the objective lens 11 andis irradiated onto the ultra high density optical disk 12.

The objective lens 11 given here has a numerical aperture (NA) of 0.85,and is designed such that aberration with respect to the optical disk 12whose substrate thickness is 0.1 mm is at a minimum. Furthermore, aphase plate 206 contains the phase shift step 206 a (FIG. 62) shown inthe second conventional example, and is designed such that the light ofwavelength λ1 passes through without being affected.

The light that was reflected by the ultra high optical disk 12 passesagain through the objective lens, is focused by the focusing lens 7, isreflected by the prism 6 and is incident on a detecting device 15. Thedetecting device 15 contains a plurality of photodetecting regions, andoutputs a signal in response to the amount of light that is received.

When recording onto and reproducing from the DVD 13, the light ofwavelength λ2 that was emitted from the light source in the module 2 ais reflected by the prism 4, passes through the prism 6, and isconverted by the focusing lens 7 to diverging light that has an optimumdegree of divergence.

Then, by changing the position of the light source of the module 2 a asgiven by A to D in the diagram, it is possible to alter the degree ofdivergence, or convert it to collimated light at the focusing lens 7.When there is no phase plate 206, if the position of the light source ofmodule 2 a is B, then the divergent light that passed through thefocusing lens 7 passes through the objective lens 11, whose numericalaperture is limited to NA 0.6 and which is designed such thataberrations with respect to the optical disk 12 whose substratethickness is 0.1 mm are at a minimum, to become diverging light whosestandard deviation of wavefront aberration is at a minimum when emittedonto the DVD 13 whose substrate thickness is 0.6 mm. The diverging lightis reflected by the mirror 8, its aberration is corrected by wavefrontconversion by the phase plate 206, is focused by the objective lens 11and irradiated onto the DVD 13.

The NA of the light that is emitted from the objective lens 11 islimited to 0.6. The light that is reflected by the DVD 13 passes againthrough the objective lens 11 and the phase plate 206, is reflected bythe mirror 8, is focused by the focusing lens 7, passes through theprism 6, is reflected by the prism 4 and is incident on the detectingdevice of the module 2 a. The detecting device of the module 2 acontains a plurality of photodetecting regions, and emits a signal inresponse to the amount of light that is received.

If the light that is incident on the objective lens 11 is diverging,then when the objective lens is driven in the tracking direction, comaaberration occurs because the light is incident on the objective lens 11at an incline. This first embodiment is provided with an objective lensdrive apparatus 44 that is capable of tilting, and coma aberration thatis caused due to driving the objective lens 11 in the tracking directioncan be cancelled out by coma aberration that occurs by tilting theobjective lens 11.

FIG. 27 shows the objective lens drive apparatus 44 that is capable oftilting the objective lens 11. FIG. 27A is a structural diagram of theobjective lens drive apparatus, and FIG. 27B schematically shows alateral view. A lens holder 33 is provided with the objective lens 11and drive coils 34 a, 34 b and 35, and these are suspended from a fixedportion 37 by wires 36.

A magnetic circuit is constituted by the drive coils 34 a, 34 b and 35,and a magnet 38. The objective lens 11 is driven in the trackingdirection (x direction) by passing an electric current through the drivecoils 35, and is driven in the focus direction by passing an electriccurrent in the same direction, and of the same value, through the drivecoils 34 a and 34 b. And, by passing different electric currents throughthe electric coils 34 a and 34 b the objective lens 11 can be tilted inthe φ direction as shown in FIG. 27B. Depending on the amount oftracking movement of the objective lens 11, coma aberration can becancelled out by tilting the objective lens 11.

Since a large coma aberration occurs when the objective lens is moved inthe tracking direction in the second conventional example, accuraterecording and reproduction is difficult. However according to thepresent embodiment, less aberrated light can be focused onto theinformation surface by tilting the objective lens, and information canbe recorded and reproduced favorably.

Fifth Embodiment

FIG. 28 is a structural diagram showing an optical head according to afifth embodiment of the present invention. It differs from the fourthembodiment in a phase plate 9, and in that the light source of themodule 2 a is in the position A. The position A of the light source ofthe module 2 a is closer to the objective lens 11 than the position B,at which the standard deviation of the wavefront aberration of the lightthat is emitted from the module 2 a is at a minimum.

FIG. 29 shows the structure of the phase plate 9. FIG. 29A is a planview of an upper surface (disk side), and FIG. 29B is a lateral view. Aphase shift step 9 a that is circular and that has a height d isconfigured on the phase plate 9. The height d is:d=2 λ1/(n1−1),whereby n1 is the refractive index of the phase plate 9 at thewavelength λ1.

During recording onto and reproducing from the ultra high densityoptical disk 12, the light of wavelength λ1 is phase shifted by 2λ(where λ is the wavelength that is used) by the phase shift step 9 a,however since this is an integer multiple of the wavelength, thewavefront of the light is not affected, and there is no light loss. Thatis to say, favorable jitter can be obtained during reproduction of theultra high density optical disk 12 and sufficient peak intensity can beobtained when recording.

In this case, if the wavelength λ that is used is determined, then thephase shift 2λ is also uniquely fixed. However if the phase shift 2λ iswithin a predetermined range with respect to a predetermined wavelengthλ that is used, then an effect can be obtained whereby the wavefront ofthe light that has a wavelength within the range 380 to 420 nm issubstantially unaffected at the phase plate 9.

More specifically, the expression:760 nm≦(n−1)×d≦840 nmcan be satisfied when the wavelength standard is 400 nm, which is withinthe range of wavelength λ1 that is 380 to 420 nm, and n is therefractive index of the substrate at a wavelength of 400 nm.

On the other hand, during recording and reproduction of the DVD 13, aphase shift of d/λ2×(n2−1)=1.2λ is generated in the light of wavelengthλ2 by the phase shift step 9 a. Since integer multiples of thewavelength can be ignored for phases of the light, if consideration isgiven only to the portion to the right of the decimal point then dcorresponds to 0.2λ. That is to say, the wavefront of the light ofwavelength λ2 is converted.

FIG. 30 shows a wavefront aberration in the case in which there is nophase plate 9 by a thin line, and the wavefront aberration in the casein which there is a phase plate 9 by a thick line. In the case in whichthere is no phase plate 9, the standard deviation of the wavefrontaberration is 77 mλ, however in the case in which there is the phaseplate 9, the standard deviation reduced to 51 mλ. This is the same as inthe second conventional example. If the standard deviation of thewavefront aberration is lower than the Marshall Standard of 70 mλ, thenthe optical head has a diffraction limit capability, and information canbe recorded and reproduced favorably.

Thus, because the degree of divergence of the light of wavelength 2 isgreater than that shown in the second conventional example, the presentfifth embodiment can get by with fewer steps on the phase plate 9, andthe configuration is greatly simplified. That is to say, fabrication ofthe phase plate is facilitated, light loss can be suppressed, andelectrical power consumption of the light source can be reduced.

Furthermore, if the light that is incident on the objective lens 11 isdivergent light, then coma aberration occurs when the objective lens 11is driven in the tracking direction. However by using the objective lensdrive apparatus 44, which is capable of tilting and which was describedin the fourth embodiment, if the objective lens 11 is tilted in responseto the amount of tracking movement, coma aberration can be cancelledout.

Thus, according to the present fifth embodiment, it is possible tosuppress the loss of light to the ultra high density optical disk 12 andthe DVD 13 using a phase plate of simple construction. Furthermore,since coma aberration can be corrected by tilting the objective lens 11,it is possible to focus light with less aberrations onto the informationsurface, and information can be recorded and reproduced favorably.

It should be noted that for simplicity, the module 2 a combines thelight source and the detecting device in a single body. However thelight source and the detecting device may also be separate bodies.

Sixth Embodiment

FIG. 31 shows a structural diagram of an optical head according to asixth embodiment of the present invention. It differs from the fourthembodiment in the light source of the module 2 a being in the positionC, a phase plate 16, and in that a tilting apparatus for the objectivelens 11 not being necessary.

The position of the light source of the module 2 a is at position C,which is substantially the mid point between position D and position B.That is to say, the position C is a position that is substantiallymidway between the position D, from which point the light of wavelengthλ2 that passes through the focusing lens 7 is collimated light, and theposition B, from which point the light of wavelength λ2 that passesthrough the focusing lens 7 passes through the objective lens 11, whosenumerical aperture is limited to 0.6 and which is designed such thataberration of light is at a minimum with respect to the optical disk 12whose substrate thickness is 0.1 mm, to have minimum wavefrontaberration when irradiated onto the DVD whose substrate thickness is 0.6mm.

Since the degree of divergence of the diverging light that is incidenton the objective lens 11 is less than when the light source of themodule 2 a is in position B, even if the objective lens 11 is driven inthe tracking direction, the occurrence of coma aberration is negligible.That is, since there is no necessity to provide a tilting apparatus fortilting the objective lens 11, the system configuration can be simple.

FIG. 32 shows a structure of a phase plate 16. FIG. 32A is a plan viewof an upper surface (disk side), and FIG. 32B is a lateral view. A phaseshift step 16 a that provides concentric ring-shaped steps d, 2 d, 3 dand 4 d, whose single step height is d, is configured on the phase plate16. When the refractive index of the phase plate 16 at the wavelength λ1is set to n1, the height d is determined by:d=2 λ1/(n1−1).

Furthermore, as described in the fifth embodiment, if the phase shift iswithin a predetermined range, than an effect can be obtained whereby thewavefront of the light that has a wavelength that is within the range380 to 420 nm is substantially unaffected at the phase plate.

More specifically, the expression:760 nm≦(n−1)×d≦840 nmcan be satisfied when the wavelength standard is set to 400 nm, which iswithin the range of wavelength λ1 that is 380 to 420 nm, and n is therefractive index of the substrate at a wavelength of 400 nm.

During recording and reproducing of the ultra high density optical disk12, the light of wavelength λ1 is phase shifted by 2λ by the height d,however since this is an integer multiple of the wavelength, thewavefront of the light is not affected, and there is no light loss. Thatis to say, a favorable jitter is obtained when reproducing from theultra high density optical disk 12 and sufficient peak intensity can beobtained when recording.

On the other hand, during recording and reproduction of the DVD 13, theheight d generates a phase shift of d/λ2×(n2−1)=1.2 λ in the light ofwavelength λ2. Since integer multiples of the wavelength can be ignoredfor phases of the light, if consideration is given only to the portionto the right of the decimal point, then d corresponds to 0.2λ.Similarly, heights 2 d, 3 d, and 4 d correspond to phase shifts of 0.4λ,0.6λ and 0.8λ. That is to say, the wavefront of the light of wavelengthλ2 is converted.

FIG. 33 shows a wavefront aberration in the case in which there is nophase plate 16 by a thin line, and the wavefront aberration in the casein which there is a phase plate 16 by a thick line. The width and heightof the steps of the phase plate 16 a are configured so as to correct thewavefront aberration of the thin line. Thus, while the standarddeviation of the wavefront aberration is 490 mλ when there is no phaseplate 16, it reduces to 58 mλ when the phase plate 16 is in place. Ifthe standard deviation of the wavefront aberration is lower than theMarshall Standard of 70 mλ, then the optical head has a diffractionlimit capability, and information can be recorded and reproducedfavorably.

Thus, since the coma aberration that is generated when the objectivelens 11 is driven in the tracking direction can be suppressed accordingto the present embodiment, it is possible to omit the tilting apparatusof the objective lens 11, the optical head can be made straightforward,and the system configuration also simplified. Furthermore, because it ispossible to focus light with less aberrations onto the informationrecording surfaces of the ultra high density optical disk 12 and the DVD13, information can be recorded and reproduced favorably.

It should be noted that that the present embodiment is described usingan example in which the phase shift step has a height of 4 d, however itis also possible to use heights of 5 d, 6 d or greater.

Furthermore, even if the position of the light source of the module 2 ais between C and D, if the configuration of the width and height of thephase shift step is changed so as to correct the wavefront aberration,then the same effect can be obtained.

Furthermore, for simplicity the module 2 a combines the light source andthe photodetector in a single body, however the light source and thephotodetector may also be separate bodies.

Furthermore, although in the present embodiment, the coma aberration issuppressed to the extent that tilting the objective lens 11 is notnecessary, however it is possible to add a tilt drive to the objectivelens 11. By adding tilting, the tilt margin of the optical disk isenlarged, and even disks that are warped to a large extent can befavorably recorded and reproduced.

Seventh Embodiment

An optical head according to the seventh embodiment of the presentinvention is shown in FIG. 34. It differs from the sixth embodiment inthat there is no module for the DVD 13, only a light source 2, and inthat it has a phase shift step 17. The light source 2 is set in aposition such that the light of wavelength λ2 that passes through thefocusing lens 7 is collimated light. Thus, since the light that wasreflected by the DVD 13 can be focused on the detecting device 15 it ispossible to use the detecting device for both the ultra high densityoptical disk 12 and for the DVD 13. That is, the number of parts can bereduced, and a cost reduction achieved. Furthermore, since the lightthat is incident on the objective lens 11 is collimated light, there isno necessity for the tilting apparatus for the objective lens 11, theoptical head is simplified, and coma aberration does not occur even whenthe objective lens 11 is driven in the tracking direction.

FIG. 35 shows the structure of the phase plate 17. FIG. 35A is a planview from an upper surface (disk side), and FIG. 35B is a lateral view.A phase shift step 17 a that has concentric ring-shaped steps d, 2 d, 3d and 4 d, whose single step height is d, is configured on the phaseplate 17. When the refractive index of the phase plate 17 at thewavelength λ1 is set to n1, the height d is determined by:d=2 λ1/(n1−1).The configuration in FIG. 35B has an increased number of steps in theradial direction than that of the structure in FIG. 32B of the sixthembodiment.However since the minimum width is in the order of 12 μm, itis easier to fabricate.

During recording and reproduction of the ultra high density optical disk12, the light of wavelength λ1 is phase shifted by 2λ by the height d,however since this is an integer multiple of the wavelength, thewavefront of the light is not affected, and there is no light loss. Thatis to say, a favorable jitter can be obtained during reproduction fromthe ultra high density optical disk 12 and sufficient peak intensity canbe obtained when recording.

Furthermore, as described in the fifth embodiment, if the phase shift 2λis within a predetermined range, then an effect can be obtained wherebythe wavefront of the light that has a wavelength within the range 380 to420 nm is substantially unaffected at the phase plate.

More specifically, the expression:760 nm≦(n−1)×d≦840 nmcan be satisfied when the wavelength standard is 400 nm, which is withinthe range of wavelength λ1 that is 380 to 420 nm, and n is therefractive index of the substrate at a wavelength of 400 nm.

On the other hand, during recording and reproduction of the DVD 13, theheight d generates a phase shift of d/λ2×(n2−1)=1.2λ in the light ofwavelength λ2. Since integer multiples of the wavelength can be ignoredfor phases of the light, when consideration is given only to the portionto the right of the decimal point, d corresponds to 0.2λ. Similarly,heights 2 d, 3 d, and 4 d correspond to phase shifts of 0.4λ, 0.6λ and0.8λ. That is to say, the wavefront of the light of wavelength λ2 isconverted.

FIG. 36 shows a wavefront aberration in the case in which there is nophase plate 17 by a thin line, and a wavefront aberration in the case inwhich there is a phase plate 17 by a thick line. The width and height ofthe steps of the phase plate 17 are configured so as to correct thewavefront aberration of the thin line. Thus, while the standarddeviation of the wavefront aberration is 780 mλ when there is no phaseplate 17, it reduces to 58 mλ when the phase plate 17 is in place. Ifthe standard deviation of the wavefront aberration is lower than theMarshall Standard of 70 mλ, then the optical head has a diffractionlimit capability, and information can be recorded and reproducedfavorably.

In this manner, by causing the light that is incident on the objectivelens 11 to be collimated light according to the present embodiment, thenecessity of the tilting apparatus for the objective lens 11 disappears,the optical head can be made more straightforward, and the systemconfiguration also simplified. Furthermore, because it is possible tofocus light with less aberrations onto the information recordingsurfaces of the ultra high density optical disk 12 and the DVD 13,information can be recorded and reproduced favorably.

It should be noted that that the present embodiment is described usingan example in which the phase shift step has a height of 4 d, however itis also possible to use heights of 5 d, 6 d or greater.

Eighth Embodiment

An optical head according to the eighth embodiment is shown in FIG. 37.It differs from the seventh embodiment in the provision of a mirror 19,and a phase plate 18, but the configuration up to where the light thatis emitted from the light source becomes collimated light, and theconfiguration in which the light that was reflected by the optical disk12 is incident on the detecting device 15 are the same as in the seventhembodiment.

As shown in FIG. 38, the mirror 19 has a flat reflecting surface 19 aand a curved reflecting surface 19 b, which has a radius of curvature R.The reflecting surface 19 a is constituted by a dichroic film thattotally reflects a light 1 a of wavelength λ1 remain parallel withrespect to the objective lens 11, while allowing a light 2 b ofwavelength λ2 to completely pass.

Furthermore, the reflective surface 19 b totally reflects and convertsthe light 2 b of wavelength λ2 into diverging light that has a degree ofconvergence that is optimal for the objective lens 11. The phase shiftsteps of the phase plate 18 are set in response to the degree ofdivergence. For example, the degree of divergence and the phase plate 18can be the same as in the sixth embodiment.

Thus with such a configuration, since the coma aberration that occurswhen the objective lens 11 is driven in the tracking direction can besuppressed to an insignificant amount, it is possible to focus lightwith less aberrations onto the information recording surfaces of theultra high density optical disk 12 and the DVD 13, and information canbe recorded and reproduced favorably. Furthermore, costs can be reducedsince the detecting devices can be combined into one.

Furthermore, since the number of steps is fewer, and the width of thesteps is wider than in the seventh embodiment, manufacture isfacilitated, fabrication to shape as designed is possible, and it ispossible to reduce light loss.

Ninth Embodiment

A description of the ninth embodiment of the present invention uses FIG.39. FIG. 39 shows a structural diagram of the phase plate 18. FIG. 39Ais a lateral view, and FIG. 39B is a view of a rear surface. The phaseplate 18 is constituted by a phase shift step 18 a on an upper surface(disk side), and a chromatic aberration correction hologram 18 b thathas the power of a convex lens on the rear surface (side furthest fromthe disk).

The chromatic aberration correction hologram 18 b is disclosed in detailin the Patent Document 3 (JP 2001-60336A). This corrects chromaticaberration by canceling out the aberration that is caused at theobjective lens by a shift in the wavelength of the light of wavelengthλ1, by changing the diffraction angle of a diffraction grating. Byconfiguring the phase plate 18 and the chromatic aberration correctionhologram 18 b as a single piece, it is possible to correct chromaticaberration without supplementing new parts.

It should be noted that it is possible to obtain the same effect byconfiguring the chromatic aberration correction hologram into a singlepiece with the phase plates that are described in the fourth to eighthembodiments.

Tenth Embodiment

An optical head according to the tenth embodiment of the presentinvention is shown in FIG. 40. The ultra high density optical disk 12whose substrate thickness is 0.1 mm, the optical disk (DVD) 13 whosesubstrate thickness is 0.6 mm and the optical disk (CD) 14 whosesubstrate thickness is 1.2 mm are shown in their recording andreproduction state, and for the purpose of simplifying the description,they are drawn overlapping in the same position.

The optical head contains the light source 1 that emits light of awavelength 380 nm to 420 nm (wavelength λ1), the light source 2 thatemits light of a wavelength 630 nm to 680 nm (wavelength λ2) and thelight source 3 that emits light of a wavelength 780 nm to 820 nm(wavelength λ3).

During recording and reproduction of the ultra high density optical disk12, the light of wavelength λ1 that is emitted from the light source 1passes through the prisms 4, 5, and 6, and is converted to collimatedlight by the focusing lens 7. This collimated light is reflected by themirror 8, passes through a liquid crystal hologram 10 and the phaseplate 17, is focused by the objective lens 11, and is irradiated ontothe ultra high density optical disk 12.

Here, the objective lens 11 is designed to have an NA of 0.85, and tohandle light of wavelength λ1 and a disk whose substrate thickness is0.1 mm. Furthermore, the phase plate 17, as will be explained below, isdesigned to allow light of wavelength λ1 and λ3 to pass without beingaffected, and to convert the wavefront of the light of wavelength λ2.

Furthermore, during recording and reproduction of the ultra high densityoptical disk, the liquid crystal hologram is in a state in which avoltage is not applied (OFF), and the light passes through without beingaffected. The light that was reflected by the ultra high density opticaldisk 12 passes again through the objective lens 11, the phase plate 17and the liquid crystal hologram 10, and is reflected by the mirror 8.This reflected light is focused by the focusing lens 7, is reflected bythe prism 6, and is incident on the detecting device 15. The detectingdevice 15 contains a plurality of photodetecting regions, and outputs asignal in response to the amount of light that is received.

During recording and reproduction of the DVD 13, the light of wavelengthλ2 that is emitted from the light source 2 is reflected by the prism 4,passes through the prisms 5 and 6, and is converted to collimated lightby the focusing lens 7. This collimated light is reflected by the mirror8, passes through the liquid crystal hologram 10, is wavefront convertedby the phase plate 17, is focused by the objective lens 11, and isirradiated onto the DVD 13.

Here, the NA of the light that is emitted from the objective lens 11 islimited to 0.6. Furthermore, the phase plate 17 is designed such thatafter passing through the objective lens 11, which is designed such thataberration with respect to the disk whose substrate thickness is 0.1 mmis at a minimum, when the collimated light of wavelength λ2 isirradiated onto the optical disk whose substrate thickness is 0.6 mm,the standard deviation of the wavefront aberration is not more than 70mλ.

Furthermore, during recording and reproduction of the DVD 13, the liquidcrystal hologram is in the OFF condition, and the light of wavelength λ2passes through without being affected. The light that was reflected bythe DVD 13 passes again through the objective lens 11, the phase plate17 and the liquid crystal hologram 10, and is reflected by the mirror 8.This reflected light is focused by the focusing lens 7, is reflected bythe prism 6, and is incident on the detecting device 15.

During recording and reproduction of the CD 14, the light of wavelengthλ3 that was emitted from the light source 3 is reflected by the prism 5,passes through the prism 6, and is converted to collimated light by thefocusing lens 7. This collimated light is reflected by the mirror 8, andis wavefront converted by the liquid crystal hologram 10. Moreover, itpasses through the phase plate 17, is focused by the objective lens 11,and is irradiated onto the CD 14.

Here, the NA of the light that is emitted by the objective lens 11 islimited to 0.45. Furthermore, the phase plate 17 allows the light ofwavelength λ3 to pass without influence. Furthermore, during recordingand reproduction of the CD 14, the liquid crystal hologram is in acondition in which an electric voltage is applied (ON), and is designedsuch that, the standard deviation of the wavefront aberration is notmore than 70 mλ when the collimated light of wavelength λ3 is irradiatedonto the optical disk whose substrate thickness is 1.2 mm after passingthrough the objective lens 11.

The light that was reflected by the CD 14 again passes through theobjective lens 11, the phase plate 17 and the liquid crystal hologram10, is reflected by the mirror 8, is focused by the focusing lens 7, andis reflected by the prism 6 to be incident on the detecting device 15.

The configuration of the phase plate 17 is the same as the structure inFIG. 35. That is to say the phase shift step 17 a that has concentricring-shaped steps d, 2 d, 3 d and 4 d, whose single step height is d, isprovided on the phase plate 17.

When the refractive index of the phase plate 17 at wavelengths λ1 and λ3is n1 and n3, the height d is:d=2 λ1 /(n 1−1).The refractive indices n1 and n2 satisfy:−10 nm<λ1/(n 1−1)−λ3/(n 3−1)/2<10 nm.The wavefront of the light of wavelength λ2 can be convertedsubstantially without influencing the light of wavelength λ1 and λ3 byappropriately selecting the wavelength that is used and the material ofthe phase plate.

During recording and reproduction of the ultra high density optical disk12, the light of wavelength λ1 is phase shifted 2λ by the height d, andduring recording and reproduction of the CD 14, the phase shift of thelight of wavelength λ3 by the height d is substantially λ. When usinglight of either wavelength λ1 or λ3, the phase shift is an integermultiple of the wavelength so the wavefront of the light is unaffected,and there is no loss of light. That is, favorable jitter can be obtainedwhen replaying from the ultra high density optical disk 12 and the CD14, and sufficient peak intensity can be obtained when recording.

Furthermore, as shown in the fifth embodiment, if the phase shift 2λ iswithin a predetermined range, then an effect can be obtained whereby thewavefront of the light that has a wavelength within the range 380 to 420nm is substantially unaffected at the phase plate.

More specifically, the expression:760 nm≦(n−1)×d≦840 nmcan be satisfied when the wavelength standard is 400 nm, which is withinthe range of wavelength λ1 that is 380 to 420 nm, and n is therefractive index of the substrate at a wavelength of 400 nm.

On the other hand, during recording and reproduction of the DVD 13, aphase shift of d/λ2×(n2−1)=1.2 λ is generated in the light of wavelengthλ2. Since integer multiples of the wavelength can be ignored for phasesof the light, when consideration is given only to the portion to theright of the decimal point, d corresponds to 0.2λ. Similarly, heights 2d, 3 d, and 4 d correspond to phase shifts of 0.4λ, 0.6λ and 0.8λ. Thatis to say, the wavefront of the light of wavelength λ2 is converted.

For example, if the wavelength of the lights that are used is λ1=405 nm,λ2=650 nm and λ3=780 nm, then BK7, which is a common glass material, canbe used as the material of the phase plate, and the height of one stepof the phase shift step can be d=1.5292 μm. Since the refractive indexof BK7 is n1=1.15297, n2=1.5141 and n3=1.5107, the phase shift per stepfor the lights of wavelength λ1, λ2 and λ3 are respectively 2λ, 1.2λ andλ. That is, when using the ultra high density optical disk 12 and the CD14, the phase plate has no influence, and the wavefronts can beconverted only when using the DVD 13.

FIG. 36 shows a wavefront aberration in the case in which there is nophase plate 17 by a thin line, and the wavefront aberration in the casein which there is a phase plate 17 by a thick line. The width and heightof the steps of the phase shift step 17 a are configured so as tocorrect the wavefront aberration of the thin line. Thus, while thestandard deviation of the wavefront aberration is 780 mλ when there isno phase plate 17, it reduces to 58 mλ when the phase plate 17 is inplace. If the standard deviation of the wavefront aberration is lowerthan the Marshall Standard of 70 mλ, then the optical head has adiffraction limit capability, and information can be recorded andreproduced favorably.

FIG. 41 shows the structure of the liquid crystal hologram 10. FIG. 41Ais a plan view of an upper surface (disk side), and FIG. 41B is anenlarged cross-sectional view. A relief-shaped hologram pattern isprovided on a substrate 10 b whose refractive index is no, and atransparent electrode 10 c is formed on that face. A liquid crystal 10 ais sandwiched between transparent electrodes 10 c and 10 d.

The refractive index of the liquid crystal 10 a changes depending on thevoltage across the transparent electrode 10 c and 10 d. It has arefractive index of ne when in the state in which there is an appliedvoltage (ON), and has a refractive index of no when in the state inwhich there is no applied voltage (OFF). In the OFF condition, theliquid crystal 10 a and the substrate 10 b have equivalent refractiveindices. Although it is a simple flat plate in this case, a differencein the refractive indices is generated in the ON state, and a refractiveeffect is generated due to the hologram.

A predetermined diffraction effect can be obtained by appropriatelyselecting the combination of the material of the substrate 10 b and thematerial of the liquid crystal 10 a. The hologram has aberrations so asto cancel out wavefront aberrations that are generated when the light ofwavelength λ3 passes through the objective lens 11 and is irradiatedonto the CD 14. That is, when using the ultra high density optical disk12 and the DVD 13, if the hologram is turned to the OFF condition, thenthe lights are unaffected, and if the hologram is turned to the ONcondition, then the wavefront of the light can be converted.

Thus, according to the present embodiment, it is possible to focus lightwith less aberrations onto the information recording surfaces of theultra high density optical disk 12, the DVD 13 and the CD 14, andinformation can be favorably recorded and reproduced.

It should be noted that in the tenth embodiment of the presentinvention, a case is described in which the light of wavelength λ2 isconverted to collimated light by the focusing lens 7. However it is alsopossible to use cases in which it is converted to diverging light, suchas in the fifth and sixth embodiments.

Furthermore, recording and reproduction of the CD 14 is described usingthe liquid crystal, however the phase shift step of the presentinvention is characterized in that it does not influence the CD 14, soit is possible to use any method known in the art to record andreproduce the CD 14.

Furthermore, if the hologram pattern of the liquid crystal is configuredto cancel out the wavefront aberration that is generated by the DVD 13,then it is possible to use the liquid crystal even during recording andreproduction of the DVD 13. Moreover, it is also possible to mountindividual liquid crystal holograms for the CD 14 and the DVD 13.

Furthermore, the height of the phase shift steps of the fifth to thetenth embodiments was d=2λ1/(n1−1). However if the present invention islimited to recording onto and reproducing from the ultra high densityoptical disk 12 and the DVD 13, then it is possible to realize the samephase shift even if the height is d=λ1/(n1−1).

Furthermore, as described previously, if the phase shift is within apredetermined range, then an effect can be obtained whereby thewavefront of the light that has a wavelength within the range 380 to 420nm is substantially unaffected at the phase plate. Due to this, when therefractive index at the standard wavelength of 400 nm is n, then it isalso possible that the expression:380 nm≦(n−1)×d≦420 nmis satisfied.

In this case, since the height d generates a phase shift of 0.6λ in thelight of wavelength λ2, d, 2 d, 3 d and 4 d correspond to phase shiftsof 0.6λ, 0.2λ, 0.8λ and 0.4λ. For example, the phase shift step 16 a(FIG. 32) of the sixth embodiment becomes the same as the phase shiftstep 16 b that is shown in FIG. 42.

If done in this manner, since the height of the steps can be lowered,fabrication of the phase plate is facilitated and the manufacturing timecan be shortened. Furthermore, since it is easier to fabricate the shapeas designed, light loss is less and the effect of suppressing electricalpower consumption can be obtained.

Furthermore, the phase shift step can be formed easily by etching aglass substrate. Furthermore, it is also possible to form the phaseshift step by molding glass or resin. Furthermore, it is also possibleto form the phase shift step into a single piece with the objectivelens.

It should be noted that if using resin as the material for the phaseshift step, because chemical changes are likely to occur when thewavelength is less than 420 nm, it is preferable that the lightabsorptance ratio is not more than 5%, and more preferably is not morethan 3%. It is preferable to use amorphous polyolefins (such as Zonex orAPEL), for example.

Furthermore, a disk whose substrate thickness is 0.1 mm and whose NA is0.85 was assumed as an example of the ultra high density optical disk,however it is not limited to this.

Furthermore, no particular method is described for limiting the apertureof the light. However there are methods in which a wavelength selectingfilter (not shown) is vapor deposited on the phase plate 17 or theobjective lens 11, or in which a separate glass filter is provided.Furthermore, it is also possible to restrict the light by providing anaperture on the light path that is traveled only by light of eachwavelength (between the light source and the prism).

Eleventh Embodiment

An optical head according to the eleventh embodiment of the presentinvention is shown in FIG. 43. This diagram shows the ultra high densityoptical disk 12 whose substrate thickness is 0.1 mm, the optical disk(DVD) 13 whose substrate thickness is 0.6 mm and the optical disk (CD)14 whose substrate thickness is 1.2 mm. In order to simplify thedescription, these are drawn as overlapped in the same position.

The optical head contains the light source 1 of wavelength 380 nm to 420nm (λ1), the light source 2 of wavelength 630 nm to 680 nm (λ2) and thelight source 3 of wavelength 780 nm to 820 nm (λ3).

During recording and reproduction of the ultra high density optical disk12, the light of wavelength λ1 that is emitted from the light source 1passes through the prisms 4, 5, and 6, and is converted to collimatedlight by the focusing lens 7. This collimated light is reflected at areflecting surface 67 a of a dichroic mirror 67, passes through thephase plate 17, is focused by an objective lens 39 and is irradiatedonto the ultra high density optical disk 12.

Here, the reflecting surface 67 a is constituted by a dichroic film thattotally reflects the light of wavelength λ1 and λ2, and causes the lightof wavelength λ3 to completely pass. The phase plate 17 is the same asthe phase plate that was used in the seventh embodiment. Furthermore,the objective lenses 39 and 45, and the phase plate 17 are mounted in alens holder 33.

The light that was reflected by the ultra high density optical disk 12passes again through the objective lens 39 and the phase plate 17, andis reflected by the reflecting surface 67 a of the dichroic mirror 67.This reflected light is focused by the focusing lens 7, and is reflectedby the prism 6 to be incident on the detecting device 15. The detectingdevice 15 contains a plurality of photodetecting regions, and outputs asignal in response to the amount of light that is received.

During recording and reproduction of the DVD 13, the light of wavelengthλ2 that is emitted from the light source 2 is reflected by the prism 4,passes through the prisms 5 and 6, and is converted to collimated lightby the focusing lens 7. This collimated light is reflected by thereflecting surface 67 a of the dichroic mirror 67, is wavefrontconverted by the phase plate 17, is focused by the objective lens 39 andis irradiated onto the DVD 13.

The light that was reflected by the DVD 13 passes again through theobjective lens 39 and the phase plate 17, and is reflected by thereflecting surface 67 a of the dichroic mirror 67. This reflected lightis focused by the focusing lens 7, and is reflected by the prism 6 to beincident on the detecting device 15.

During recording and reproduction of the CD 14, the light of wavelengthλ3 that was emitted from the light source 3 is reflected by the prism 5,passes through the prism 6 and is converted to collimated light by thefocusing lens 7. This collimated light passes through the reflectingsurface 67 a of the dichroic mirror 67, is reflected at a reflectingsurface 67 b, is focused by an objective lens 45 and is irradiated ontothe CD 14.

The light that is reflected by the CD 14 passes again through theobjective lens 45, is reflected by the reflecting surface 67 b of thedichroic mirror 67, is focused by the focusing lens 7 and is reflectedby the prism 6 to be incident on the detecting device 15.

By using separate objective lenses 39 and 45, information can berecorded and reproduced from each of the ultra high density optical disk12, the DVD 13 and the CD 14.

An objective lens drive apparatus in which the objective lenses 39 and45 are mounted in the lens holder 33 is described in detail using FIG.44. The lens holder 33 contains the objective lens 39, which is usedwhen recording onto and reproducing from the ultra high density opticaldisk 12 and the DVD 13, the objective lens 45, which is used whenrecording to and reproducing from the CD 14 and drive coils 34 a, 34 band 35, and is suspended from the fixed portion 37 by the wires 36.

A magnetic circuit is constituted by the drive coils 34 a, 34 b and 35,and a magnet 38. The objective lenses 39 and 45 are driven in thetracking direction (x direction) by passing an electric current throughthe drive coils 35, and are driven in the focus direction by passing anelectric current in the same direction, and of the same value, throughthe drive coils 34 a and 34 b.

And, by passing different electric currents through the electric coils34 a and 34 b the objective lens 39 can be tilted in the φ direction asshown in FIG. 45. With this configuration, coma aberration caused bytilting of the optical disk can be corrected by tilting the objectivelens 39.

The present embodiment differs from the third embodiment in that the twoobjective lenses 39 and 45 are lined up in the tracking direction (xdirection).

FIG. 46 shows the condition of a spot of light that is irradiated ontothe optical disk. The differential push-pull method (DPP) and the threebeam method use a main spot for reproducing information, and two subspots for tracking detection. The main spot 39 a of the objective lens39 shown in FIG. 44 is the spot in a position 57 a shown in FIG. 46. Thesub spots are in positions 57 b and 57 c and are set at an angle θ₀ thatis optimum for the play track 59 a.

In the three beam method, for example, the angle θ₀ is set such that thesub spots 57 b and 57 c are positioned at ¼ Tp (where Tp is the trackpitch of the optical disk). Furthermore, in the DPP method, the subspots57 b and 57 c are set so as to be positioned at ½ Tp. These spots movein the x-direction in accordance with the seek operation of the opticalhead, and the positions of the spots become 58 a, 58 b and 58 c.

Since the spot positions 57 a and 57 b lie on a straight line thatpasses through the rotational center O of the optical disk in the xdirection, even if the seek operation of the optical disk is performed,the angle at the play track 59 b is kept at θ₀. The spot of theobjective lens 45 is also the same.

Thus, according to the present embodiment, by lining up two objectivelenses in the tracking direction it is possible to use the DPP method orthe three beam method, which are common tracking methods, and favorabletracking detection can be carried out.

Here, common objective lenses contain more or less coma aberration thatis caused by manufacturing errors. In order to correct this, it iscommon practice to perform skew adjustment by tilting the optical axisof the objective lens with respect to the light that is incident on theobjective lens. Skew adjustment is carried out by tilting the objectivelens drive apparatus. As for the objective lens drive apparatus on whichthe two objective lenses are mounted, the objective lenses changeposition as a single body when the objective lens drive apparatus istilted. Due to this, even if skew adjustment is performed on oneobjective lens, the other lens does not necessarily reach its optimumcondition. Furthermore, it is necessary to raise the accuracy of theskew adjustment with increased optical disk recording density.

In the present embodiment, by dedicating use of the objective lens 45 tothe CD 14, which has the lowest recording density of the three opticaldisks, it is possible to separate the skew adjustment of the objectivelens 39, omitting it with respect to the objective lens 45, and thussimplify the skew adjustment. That is to say, skew adjustment of theobjective lens 39 is carried out, but dedicated skew adjustment is notnecessary for the CD 14.

With regard to the CD whose recording density is relatively low, sincethere is no particular necessity for accurate skew adjustment, evenwithout an adjustment that tilts the objective lens drive apparatus, itis sufficient to have coarse adjustment in which the objective lens 45is tilted with respect to the lens holder 33. Furthermore, since the CDuses a relatively long wavelength and a low NA, there is a large degreeof freedom in the design of the objective lens 45. By removing sineconditions, it is possible to design an objective lens 45 such as thisto suppress to a minimum the coma aberration that occurs when theobjective lens 45 is tilted. If an objective lens 45 that is designed insuch a way is used, then dedicated skew adjustment for the CD 14 can beomitted.

It should be noted that a wire suspension-type objective lens driveapparatus was used in describing the present embodiment. However asimilar effect of simplifying the skew adjustment can be obtained evenif two objective lenses are mounted on an axially oscillating-typeobjective lens drive apparatus.

Furthermore, since the CD 14 has a low NA, the outside diameter of theobjective lens 45 can be designed to be smaller. That is, it is possibleto arrange the objective lens 45 on the inner circumferential side ofthe optical disk of the objective lens 39.

This is illustrated using FIG. 47. The objective lenses 39 and 45 arearranged lined up in the tracking direction on an optical head 62. Theultra high density optical disk 12 is fixed, sandwiched between aturntable 63 and a damper 64, and is rotated by a motor 65.

The optical head 62 rides on a traverse 66, and is capable of moving(seek operation) from the inner circumference to the outer circumferenceof the optical disk 12. The optical head 62 and the motor 65 are inclose proximity when the optical head 62 moves to the position of theinformation that is recorded at the most inner circumference of theoptical disk 12.

In this case, since the outer diameter of the objective lens 45 issmall, the objective lens 39 can move to the inner most circumferenceposition, and it is possible to read in information without problems.Furthermore, information on the inner most circumference also can bereproduced using the objective lens 45.

Furthermore, since the objective lens 45 is shifted further from thecentral position of the lens holder 33 than the objective lens 39, asshown in FIG. 45, a movement in the focus direction Z_(T) occurs whentilted. This causes the tilt control to interfere with the focuscontrol, and is not preferable from the standpoint of control stability.

On the other hand, since the objective lens 39 is positioned in thecenter (tilting center) of the lens holder 33, there is no substantialmovement in the focus direction, and control interference does notoccur. That is, with respect to the ultra high density optical disk 12and the DVD 13, with which tilting is preferable, information can berecorded and reproduced reliably and favorably using tilt control byarranging the objective lens 39 in the center of the lens holder 33.

Thus, according to the present embodiment, by arranging the objectivelens 39 that is for the ultra high density optical disk 12 and the DVD13 in the center of the lens holder, and arranging the objective lens 45for the CD 14 on the inner peripheral side of the optical disk, manyeffects can be obtained, such as simplifying skew adjustment, allowingreproduction of data on the inner most circumference of the opticaldisks and making it possible to tilt the objective lens for the ultrahigh density optical disk and the DVD.

It should be noted that if tilting is not necessary, then the drivecoils 34 a and 34 b can be interchangeable.

Furthermore, the present embodiment was explained using the phase plate17. However a liquid crystal or a hologram can be used as long as it isa means that is capable of recording and reproducing the ultra highdensity optical disk 12 and the DVD 13.

Furthermore, the present embodiment was explained using the case inwhich the objective lens 39 was used during recording and reproductionfrom the ultra high density optical disk and the DVD 13, and theobjective lens 45 was used during recording and reproduction of the CD14. However even if a dedicated objective lens is used for the ultrahigh density optical disk 12, and an objective lens is used for the DVD13 and the CD 14, then the DPP method or the three beam method can beused, and a similar, or equivalent effect can be obtained. Furthermore,at this time, it goes without saying that it is also possible to recordand reproduce just of one of either of the CD 14 or the DVD 13.

Twelfth Embodiment

An optical head according to the twelfth embodiment of the presentinvention is shown in FIG. 48. It differs from the eleventh embodiment,in an objective lens 68, and in that it contains a detecting device 69that is for detecting the tilt of the optical disk. FIG. 48 shows therecording and reproducing state of the ultra high density optical disk12, and shows the manner in which the ultra high density optical disk istilted.

The light of wavelength λ1 that is emitted from the light source 1 isfocused by the objective lens 39, and is irradiated onto the ultra highdensity optical disk 12 to perform recording and reproduction. At thesame time, the light of wavelength λ3 that is emitted from the lightsource 3 is incident on an objective lens 68, which is described later,and pass through remain collimated light only in a ring-shaped region,after which it is irradiated onto the ultra high density optical disk12. The direction of light that is reflected from the ultra high densityoptical disk 12 that is tilted is changed, and is detected by thedetecting device 69.

In the diagram, the reflected light of the ring-shaped region isindicated by hatching. Here, a cross-sectional view of the objectivelens 68 is shown in FIG. 49A, and as shown in FIG. 49B, a rear surfaceview (the opposite side to the disk) contains a ring-shaped region 77 afor tilt detection. Collimated light that passes through the region 77 apasses straight though, as is, without being focused. Light that passesthrough regions other than 77 a is optimized for the CD 14. Duringrecording and reproduction of the CD 14, there is a slight reduction inthe amount of light, but this causes no problems with recording andreproduction.

FIG. 50 shows the detecting device 69. The detecting device contains twodetecting regions, and the ring-shaped light that is received moves inresponse to the amount of tilt of the ultra high density optical disk12. The amount of tilt of the ultra high density optical disk 12 can bedetected by a signal difference V1−V2 that is obtained at each of thedetecting regions of the detecting device 69.

Coma aberration is generated because of warping (tilt) of the opticaldisks, which generally occurs due to manufacturing errors or age or thelike. And since high accuracy aberration properties are demanded alongwith increase in recording density, it is preferable to correct comaaberration by tilting the objective lens in order to favorably carry outrecording and reproduction. If tilt detection is carried out accordingto the present embodiment, and tilting drive carried out by theobjective lens drive mechanism that is capable of tilting that wasdescribed in the eleventh embodiment, then coma aberration can becorrected based on the tilt detection signal, and information can berecorded and reproduced favorably.

Thus, according to an embodiment of the present invention, since lightof another wavelength, which is not being used for recording orreproduction, is utilized, tilting can be detected by a simpleconfiguration, there is no necessity to attach a new tilt sensor, andcosts can be reduced. Furthermore, highly accurate tilt detection can beobtained since the tilt is detected in the vicinity of the spot that isrecording and reproducing information.

It should be noted that the present embodiment is described using thecase in which the detecting region of the detecting device 69 is dividedinto two, however if it is divided into four, then it is possible todetect tilt in the radial and tangential directions.

Furthermore, in the foregoing description, an example was given ofdetecting tilt of the ultra high density optical disk whose substratethickness is 0.1 mm using the light for the CD 14. However the presentembodiment is not limited to this, and it is also possible to detect thetilt of the DVD 13 using the light for the CD 14. Even in this case,since tilt detection is carried out using light of a wavelength that isnot recording or reproducing information, the same effect can beobtained.

Furthermore, in the present embodiment, some of the objective lens 68was given to the region for tilt detection. However it is not limited tothis, and the same effect can be obtained by opening a through hole (notshown) in the lens holder 33 that holds the objective lens 68 to passlight for tilt detection.

Furthermore, for simplicity, the detecting device 15 for recording andreproduction, and the detecting device 69 for tilt detection areseparate bodies. However they can also be a single piece.

Thirteenth Embodiment

An optical head according to the thirteenth embodiment of the presentinvention is shown in FIG. 51. This differs from the twelfth embodimentin the provision of an objective lens 79. FIG. 51 shows the manner inwhich the ultra high density optical disk 12 is recorded or reproduced,and the manner in which the ultra high density optical disk is tilted.

The light of wavelength λ1 that is emitted from the light source 1 isfocused by the objective lens 39 and irradiated onto the ultra highdensity optical disk 12 to carry out recording and reproduction. At thesame time, the light of wavelength λ3 that is emitted from the lightsource 3 is incident on the objective lens 79 and is irradiated onto theultra high density optical disk 12.

Here, the objective lens 79 is designed such that aberration of lightwith respect to a substrate thickness of 0.1 mm is minimized by an innercircumference area 79 a, and that aberration of light with respect to asubstrate thickness of 1.2 mm (CD) is minimized by an outercircumference area 79 b. During recording reproduction of the CD,recording and reproduction is performed using the spot created by theouter circumference region 79 b. At this time, light of the innercircumference region is largely unfocused, and does not affect recordingor reproduction.

On the other hand, of the light that is incident on the ultra highdensity optical disk 12, although the spot of the light of the outercircumference region 79 b is largely unfocused, the light of the innercircumference region 79 a is focused in the vicinity of the recordingsurface. The light of the inner circumference region 79 a that isreflected by the ultra high density optical disk is detected by thedetecting device 15.

In the diagram, reflected light of the inner circumference region 79 ais shown by hatching. Since focus control is carried out with respect tothe objective lens 79 during recording and reproduction of the ultrahigh density optical disk 12, if the ultra high density optical disk 12tilts, then a focus shift will occur with respect to the objective lens79. Using methods such as the astigmatization method or the knife edgemethod in the detecting device 15, if light in which a focus shift hasoccurred is detected, this can be used as a tilt detection signal.

Coma aberration is generated because of warp in optical disks, whichgenerally occurs due to, for example, manufacturing errors or age. Andsince high accuracy aberration properties are required with increasingrecording density, in order to carry out recording and reproductionfavorably, coma aberration preferably is corrected by tilting theobjective lens. According to the present embodiment, by performing tiltdetection using the detecting device 15 and by performing tilting driveusing the tilt capable objective lens drive apparatus that was describedin the eleventh embodiment, coma aberration can be corrected andinformation can be favorably recorded and reproduced.

Thus, according to the present embodiment, since light of anotherwavelength that is not recording or reproducing, is utilized, tiltingcan be detected by a simple configuration, there is no necessity toattach a new tilt sensor, and costs can be reduced. Furthermore, highlyaccurate tilt detection can be obtained since the tilt is detected inthe vicinity of the spot that is recording and reproducing information.

It should be noted that in the present embodiment, an example isdescribed in which tilt of the optical disk 12 whose substrate thicknessis 0.1 mm is detected using light for the CD 14. However, it is notlimited to this, and it is also possible to detect the tilt of the DVD13 using the light for the CD 14. Even in this case, the same effect canbe obtained because tilt is detected by utilizing light of a wavelengththat is not recording and reproducing information.

Fourteenth Embodiment

FIG. 52 shows a complete structural example of an optical disk drive 89as an optical information recording and reproduction apparatus. Anoptical disk 61 is fixed, sandwiched between the turntable 63 and thedamper 64, and is rotated by the motor (rotating system) 65, which is amoving means.

The optical head 62 that is described in any one of the fourth tothirteenth embodiments rides on the traverse (conveying system) 66,which is a moving means, and is set such that the light that is emittedcan move from the inner circumference to the outer circumference of theoptical disk. A control circuit 68 performs focus control, trackingcontrol traverse control and motor rotation control based on the signalthat is received from the optical head 62. Furthermore, it alsoreproduces information from the reproduction signal, and sends therecording signal to the optical head 62.

Fifteenth Embodiment

The fifteenth embodiment is an embodiment in which an optical head thatwas shown in the first to fourteenth embodiment is used in a computer.FIG. 53 shows a perspective view of the computer (personal computer)according to the present embodiment. In FIG. 53, a computer 100 isconstituted by an optical disk drive (optical information recording andreproduction apparatus) 101, a keyboard 103 to input information, and amonitor 102 for displaying information. The optical disk drive 101 isprovided with any of the optical heads described in the first tofourteenth embodiments.

Since the computer 100 is provided with the optical disk drive 101 thatincludes any of the optical heads described in the first to fourteenthembodiments as an external recording device, information can be recordedand reproduced reliably for different types of optical disks, and it canbe used over a wide range of applications.

Furthermore, it is possible to make use of the high capacity of opticaldisks to back up the computer hard disk. Furthermore, by making use ofthe low cost and portability of the media (optical disk), and itsinterchangeability, in which its information can be read out on anotheroptical disk drive, programs or data can be exchanged with other people,or can be for personal use. Furthermore, it can also handle pre-existingmedia such as DVDs or CDs.

Sixteenth Embodiment

The sixteenth embodiment is an embodiment in which an optical head shownin the first to fourteenth embodiments is used in an optical diskrecorder (image recording device). FIG. 54 shows a perspective view ofthe optical disk recorder according to the present embodiment. Anoptical disk recorder 110 is used when connected to a monitor 111 thatis for displaying images recorded on the optical disk recorder 110.

Since the optical disk recorder 110 is provided with an optical diskdrive that includes an optical head described in any of the first tofourteenth embodiments, information can be reliably recorded onto andreproduced from different types of optical disks, and it can be usedover a wide range of applications.

Furthermore, the optical disk recorder 110 records images onto themedia, which then can be reproduced when desired. There is no necessityto rewind the optical disk like a tape after recording and afterreproduction, and chasing playback, in which the start of a program canbe reproduced while recording that program, and simultaneousrecording/replaying, in which a pre-recorded program is reproduced whilerecording another program, are possible.

Moreover, by making use of the low cost and portability of the media(optical disk), and its interchangeability, in which its information canbe read out on another optical disk drive, programs or data can beexchanged with other people, or can be for personal use. Furthermore, italso can handle pre-existing media such as DVDs or CDs.

It should be noted that the description here is of an optical diskrecorder provided with only an optical disk drive, however an internalhard disk can also be provided, as can a video tape that has a recordingand reproduction function. In this manner, temporary saving or backup ofimages is facilitated.

Seventeenth Embodiment

The seventeenth embodiment is an embodiment in which optical heads shownin the first to fourteenth embodiments are used in an optical diskplayer (image reproduction apparatus). FIG. 55 shows a perspective viewof the optical disk player according to the present embodiment. Anoptical disk player 121 is provided with a liquid crystal monitor 120,and can display images that are recorded on an optical disk on theliquid crystal monitor.

Since the disk player 121 has an internal optical disk drive thatincludes an optical head described in any of the first to fourteenthembodiments, information can be recorded onto and reproduced fromdifferent types of optical disks reliably, and it can be used over awide range of applications.

Furthermore, the optical disk player can reproduce images, which arerecorded onto the media, when desired. There is no necessity to rewindthe optical disk like a tape after reproduction, and images can beaccessed and reproduced at a desired location. Furthermore, it also canhandle pre-existing media such as DVDs or CDs.

Eighteenth Embodiment

The eighteenth embodiment is an embodiment in which an optical headshown in the first to fourteenth embodiments is used in a server. FIG.56 is a perspective view of the server according to the presentembodiment.

A server 130 is provided with an optical disk drive 131, a monitor 133for displaying information and a keyboard 134 to input information, andis connected to a network 135.

Since the server 130 has an inbuilt optical disk drive that includes anoptical head described in any of the first to fourteenth embodiments,information can be and reproduced from different types of optical disksreliably, and the server can be used over a wide range of applications.

Furthermore, making use of the large capacity of optical disks,information (such as images, speech, moving images, HTML text and textdocuments) that is recorded on the optical disk is transmitted inresponse to a demand from the network 135. Furthermore, information thatis sent from the network is recorded in the requested position.Furthermore, since it is also possible to reproduce information that isrecorded on pre-existing media, such as CDs and DVDs, it is alsopossible to transmit that information.

Nineteenth Embodiment

The nineteenth embodiment is an embodiment in which an optical headshown in the first to fourteenth embodiments is used in a car navigationsystem. FIG. 57 shows a perspective view of the car navigation systemaccording to the present embodiment. A car navigation system 140 has aninternal optical disk drive that is connected to and is used with aliquid crystal monitor 141 that displays topographical and destinationinformation.

Since the car navigation system 140 is provided with an optical diskdrive that includes an optical head described in any of the first tofourteenth embodiments, information can be recorded and reproduced fromdifferent types of optical disks reliably, and it can be used over awide range of applications.

Furthermore, the car navigation system 140 calculates its presentposition based on information from map information recorded on a medium,a geo-positioning system (GPS) or a gyroscope, a speedometer and anodometer, and displays that position on the liquid crystal monitor.

Furthermore, if the destination is input, the system calculates theoptimum route to the destination based on the map information and theroad information, and displays this on the liquid crystal monitor.

By using a large capacity optical disk to record the map information, itis possible to provide detailed road information covering a wide area ona single disk. Furthermore, information about restaurants, conveniencestores and gasoline stands that are in the vicinity of the roads alsocan be provided simultaneously, contained on the optical disk.

Moreover, with the passage of time, road information becomes old andinaccurate. However since optical disks are interchangeable, and themedia is cheap, the latest information can be obtained by substitutionwith a disk containing the newest road information.

Furthermore, since the car navigation system can handle the recordingand reproduction of pre-existing media such as DVDs and CDs, it ispossible to watch movies or listen to music inside the vehicle.

INDUSTRIAL APPLICABILITY

Since the present invention according to the embodiments above reliablycan record and reproduce information from optical disks that havedifferent substrate thicknesses such as high density optical disks whosesubstrate thickness is thin, and DVDs and CDs, it can be applied incomputers, image recording devices, image reproducing devices, serversand car navigation systems.

1. An optical element, comprising: a substrate in which grooves areformed; wherein the expression:380 nm≦(n−1)×d≦420 nm is satisfied where n is a refractive index of thesubstrate at a wavelength of 400 nm, and d (nm) is a depth of one stepof the grooves; wherein the grooves are formed in four steps of depth d,depth 2d, depth 3d and depth 4d; wherein the depth of the grooves islined up in the order: depth 2d, depth 4d, depth d, depth 3d, or in theorder: depth 3d, depth d, depth 4d, depth 2d; and wherein when light ofa wavelength λ2 in a range of 630 nm to 680 nm passes through thegrooves, with respect to each of the grooves, a fractional value smallerthan a decimal point of a value obtained by dividing a light pathdifference attributable to the grooves by the wavelength λ2 iscalculated, and when the calculated fractional values correspondingrespectively to the grooves are arranged in an order in which thegrooves are lined up, the fractional values are in an order ascending ordescending in a stepwise manner.
 2. The optical element according toclaim 1; wherein the grooves are formed in concentric ring-shapes. 3.The optical element according to claim 1; wherein the grooves areadjacent via a portion in which no grooves are formed, and the width ofeach step of the grooves is substantially the same as the width of theportion in which no grooves are formed.
 4. An optical head, comprising:a first light source that emits light of a first wavelength, that atleast either records onto or reproduces information from a firstinformation recording medium; a second light source that emits light ofa second wavelength, that at least either records onto or reproducesinformation from a second information recording medium; focusing meansfor focusing light that is emitted from the first light source and fromthe second light source; an optical element that passes light of thefirst wavelength and diffracts light of the second wavelength; andphotodetecting means for detecting light of the first wavelength andlight of the second wavelength; wherein light of the first wavelengthand light of the second wavelength pass through the optical element,after which they are focused by the focusing means and are irradiatedonto the information recording media; wherein the optical element is anoptical element in which grooves are formed in a substrate; wherein theexpression:380 nm≦(n−1)×d≦420 nm is satisfied, where n is a refractive index of thesubstrate at a wavelength of 400 nm, and d (nm) is a depth per step ofthe grooves; wherein the grooves are formed in four steps of depth d,depth 2 d, depth 3 d and depth 4 d; and wherein the photodetecting meansdetects light that is at least either reflected or diffracted by theinformation recording media; wherein the depth of the grooves is linedup in the order: depth 2 d, depth 4 d, depth d, depth 3 d, or in theorder: depth 3 d, depth d, depth 4 d,depth 2 d; and wherein when lightof a wavelength λ2 in a range of 630 nm to 680 nm passes through thegrooves, with respect to each of the grooves, a fractional value smallerthan a decimal point of a value obtained by dividing a light pathdifference attributable to the grooves by the wavelength λ2 iscalculated, and when the calculated fractional values correspondingrespectively to the grooves are arranged in an order in which thegrooves are lined up. the fractional values are in an order ascending ordescending in a steowise manner.
 5. The optical head according to claim4, wherein the second wavelength is 1.5 to 1.8 times the length of thefirst wavelength.
 6. The optical head according to claim 4, wherein thegrooves of the optical element are formed on a face that is close to thefocusing means.
 7. The optical head according to claim 4, wherein forlight of the second wavelength that is diffracted by the opticalelement, the light that diverges with respect to incident light isstronger than the light that converges with respect to incident light.8. The optical head according to claim 4, wherein the optical elementcorrects the aberration to not more than 70 mλ when light of the secondwavelength that is diffracted by the optical element is focused on aninformation surface of a second information recording medium.
 9. Anoptical head comprising: a first light source that emits light of afirst wavelength, that at least either records onto or reproducesinformation from a first information recording medium; a second lightsource that emits light of a second wavelength, that at least eitherrecords onto or reproduces information from a second informationrecording medium; a third light source that emits light of a thirdwavelength, that at least either records onto or reproduces informationfrom a third information recording medium; focusing means for focusinglight that is emitted from the first light source, from the second lightsource and from the third light source; a first optical element thatpasses light ofthefirst wavelength and diffracts light of the secondwavelength and the third wavelength; and photodetecting means fordetecting light of the first wavelength, light of the second wavelengthand light of the third wavelength; wherein light of the firstwavelength, light of the second wavelength and light of the thirdwavelength pass through the optical element, after which they arefocused by the focusing means and are irradiated onto the informationrecording media; wherein the first optical element is an optical elementin which grooves are formed in a substrate; wherein the expression:380 nm≦(n−1)×d≦420 nm is satisfied where n is a refractive index of thesubstrate at a wavelength of 400 nm, and d (nm) is a depth of one stepof the grooves; wherein the grooves are formed in four steps of depth d,depth 2 d, depth 3 dand depth 4 d; wherein the photodetecting meansdetects light that is at least either reflected or diffracted by theinformation recording media; wherein the depth of the grooves is linedup in the order: depth 2 d, depth 4 d, depth d, depth 3 d, or in theorder: depth 3 d, depth d, depth 4 d, depth 2 d; wherein when linht of awavelength λ2 in a range of 630 nm to 680 nm passes throunh the grooves,with respect to each of the nrooves, a fractional value smaller than adecimal point of a value obtained by dividing a light path differenceattributable to the grooves by the wavelength λ2 is calculated, and whenthe calculated fractional values corresponding respectively to thegrooves are arranged in an order in which the grooves are lined up. thefractional values are in an order ascending or descending in a stepwisemanner.
 10. The optical head according to claim 9, wherein the secondwavelength is 1.5 to 1.8 times the length of the first wavelength; andwherein the third wavelength is 1.8 to 2.2 times the length of the firstwavelength.
 11. The optical head according to claim 9, wherein, when afirst region is a substantially circle-shaped region in the centralvicinity of the first optical element, a second region is asubstantially ring-shaped region that surrounds the first region, and athird region is a region on the outside of the second region, light ofthe first wavelength passes through the first, second and third region,light of the second wavelength passes through the first and secondregion, and light of the third wavelength passes through the firstregion.
 12. The optical head according to claim 9, wherein for light ofthe second wavelength and third wavelength that are diffracted by thefirst optical element, the light that diverges is stronger than thelight that converges with respect to incident light.
 13. The opticalhead according to claim 9, further comprising: phase correcting meansfor correcting the aberration of light of the second wavelength that isdiffracted by the first optical element to not more than 70 mλ whenlight of the second wavelength is focused on the information surface ofthe second information recording medium, and for correcting theaberration of light of the third wavelength that is diffracted by thefirst optical element to not more than 70 mλ when light of the thirdwavelength is focused on the information surface of the thirdinformation recording medium; wherein the phase correcting means doesnot change the phase of light of the first wavelength; and wherein thephase correcting means is provided in the light path between the lightsources and the optical information recording medium.
 14. The opticalhead according to claim 9, further comprising: a second optical elementthat passes light of the first wavelength and light of the thirdwavelength, and diffracts light of the second wavelength; wherein lightof the first wavelength, light of the second wavelength and light of thethird wavelength pass through the two optical elements, after which theyare focused by the focusing means, and irradiated onto the opticalinformation recording medium.
 15. The optical head according to claim 9,further comprising: a second optical element that passes light of thefirst wavelength and light of the third wavelength, and diffracts lightof the second wavelength; wherein light of the first wavelength, lightof the second wavelength and light of the third wavelength pass throughthe two optical elements, after which they are focused by the focusingmeans, and irradiated onto the optical information recording medium;wherein the second optical element is an optical element in whichgrooves are formed in a substrate; wherein the expression:760 nm≦(n−1)×d≦840 nm is satisfied, where n is a refractive index of thesubstrate at a wavelength of 400 nm, and d (nm) is a depth per step ofthe grooves; and wherein the grooves are formed in two steps of depth dand depth 2 d.
 16. The optical head according to claim 9, furthercomprising: a second optical element that passes light of the firstwavelength and light of the third wavelength, and diffracts light of thesecond wavelength; wherein light of the first wavelength, light of thesecond wavelength and light of the third wavelength pass through the twooptical elements, after which they are focused by the focusing means,and irradiated onto the optical information recording medium; whereinthe second optical element is an optical element in which grooves areformed in a substrate; wherein the expression:760 nm≦(n−1)×d≦840 nm is satisfied, where n is a refractive index of thesubstrate at a wavelength of 400 nm, and d (nm) is a depth per step ofthe grooves; and wherein the grooves are formed in three steps of depthd, depth 2 d and depth 3 d.
 17. The optical head according to claim 9,further comprising: a second optical element that passes light of thefirst wavelength and light of the third wavelength, and diffracts lightof the second wavelength; wherein light of the first wavelength, lightof the second wavelength and light of the third wavelength pass throughthe two optical elements, after which they are focused by the focusingmeans, and irradiated onto the optical information recording medium; andwherein the first optical element and the second optical element areformed on a top and a rear of a single substrate.
 18. The optical headaccording to claim 13 or 14, further comprising: a second opticalelement that passes light of the first wavelength and light of the thirdwavelength, and diffracts light of the second wavelength; wherein lightof the first wavelength, light of the second wavelength and light of thethird wavelength pass through the two optical elements, after which theyare focused by the focusing means, and irradiated onto the opticalinformation recording medium; and wherein the first optical element andthe second optical element are formed on a top and a rear of a singlesubstrate, and the face on which the second optical element is formed,of the two faces of the single substrate, is closer to the focusingmeans.
 19. The optical head according to claim 9, further comprising: asecond optical element that passes light of the first wavelength andlight of the third wavelength, and diffracts light of the secondwavelength; wherein light of the first wavelength, light of the secondwavelength and light of the third wavelength pass through the twooptical elements, after which they are focused by the focusing means,and irradiated onto the optical information recording medium; andwherein the first and second optical elements correct the aberration oflight of the second wavelength that is diffracted by the first andsecond optical elements to not more than 70 mλ when that light isfocused onto the information surface of the second information recordingmedium; and correct the aberration of light of the third wavelength λ3that is diffracted by the first optical element to not more than 70 mλwhen that light is focused on the information surface of the thirdinformation recording medium.
 20. The optical head according to claim 9,wherein, when a distance between the surface of the first informationrecording medium on the focusing means side and the tip of the focusingmeans on the side of the first information recording medium is WD1 whenlight of the first wavelength is irradiated onto the first informationrecording medium, and a distance between the surface of the secondinformation recording medium on the focusing means side and the tip ofthe focusing means on the side of the second information recordingmedium is WD2 when light of the second wavelength is irradiated onto thesecond information recording medium, and a distance between the surfaceof the third information recording medium on the focusing means side andthe tip of the focusing means on the side of the third informationrecording medium is WD3 when light of the third wavelength is irradiatedonto the third information recording medium, a difference between themaximum value and the minimum value of WD1, WD2 and WD3 is smaller thanthe maximum value of the diameter of the focusing means.
 21. The opticalhead according to claim 9, wherein, when a distance between the surfaceof the first information recording medium on the focusing means side andthe tip of the focusing means on the side of the first informationrecording medium is WD1 when light of the first wavelength is irradiatedonto the first information recording medium, and a distance between thesurface of the second information recording medium on the focusing meansside and the tip of the focusing means on the side of the secondinformation recording medium is WD2 when light of the second wavelengthis irradiated onto the second information recording medium, and adistance between the surface of the third information recording mediumon the focusing means side and the tip of the focusing means on the sideof the third information recording medium is WD3 when light of the thirdwavelength is irradiated onto the third information recording medium,WD1, WD2 and WD3 are substantially equivalent.
 22. The optical headaccording to claim 4 or 9, further comprising: a converter forconverting a plurality of signals, which are received in parallel andare output from the photodetecting means into a serial signal.
 23. Theoptical head according to claim 4, or 9, further comprising: a converterfor converting a plurality of signals, which are received in paralleland are output from the photodetecting means, into a serial signal;wherein the serial signal is an electrical signal.
 24. The optical headaccording to claim 4 or 9 further comprising: a first converter forconverting a plurality of signals, which are output from thephotodetecting means and received in parallel, into a serial signal; anda second converter for receiving the electric signal that is output fromthe first converter and for converting the electric signal into anoptical signal.
 25. An optical information recording and reproductionapparatus, comprising: an optical head that includes; a first lightsource that emits light of a first wavelength, that at least eitherrecords onto or reproduces information from a first informationrecording medium; a second light source that emits light of a secondwavelength, that at least either records onto or reproduces informationfrom a second information recording medium; focusing means for focusinglight that is emitted from the first light source and from the secondlight source; an optical element that passes light of the firstwavelength and diffracts light of the second wavelength; andphotodetecting means for detecting light of the first wavelength andlight of the second wavelength, further comprising: moving means formoving the information recording medium and the optical head relative toeach other; wherein light of the first wavelength and light of thesecond wavelength pass through the optical element, after which they arefocused by the focusing means and are irradiated onto the informationrecording media; wherein the optical element is an optical element inwhich grooves are formed in a substrate; wherein the expression:380 nm≦(n−1)×d≦420 nm is satisfied, where n is a refractive index of thesubstrate at a wavelength of 400 nm, and d (nm) is a depth per step ofthe grooves; wherein the grooves are formed in four steps of depth d,depth 2 d, depth 3 d and depth 4 d; and wherein the photodetecting meansdetects light that is at least either reflected or diffracted by theinformation recording media; wherein the depth of the grooves is linedup in the order: depth 2 d, depth 4 d, depth d, depth 3 d, or in theorder: depth 3 d, depth d, depth 4 d, depth 2 d; and wherein when linhtof a wavelength λ2 in a range of 630 nm to 680 nm passes throunh thegrooves, with respect to each of the nrooves, a fractional value smallerthan a decimal point of a value obtained by dividing a light pathdifference attributable to the grooves by the wavelength λ2 iscalculated, and when the calculated fractional values correspondingrespectively to the grooves are arranged in an order in which thegrooves are lined up. the fractional values are in an order ascending ordescending in a stepwise manner.
 26. An optical information recordingand reproduction apparatus, comprising: an optical head that includes; afirst light source that emits light of a first wavelength, that at leasteither records onto or reproduces information from a first informationrecording medium; a second light source that emits light of a secondwavelength, that at least either records onto or reproduces informationfrom a second information recording medium; a third light source thatemits light of a third wavelength, that at least either records onto orreproduces information from a third information recording medium;focusing means for focusing light that is emitted from the first lightsource, from the second light source and from the third light source; afirst optical element that passes light of the first wavelength anddiffracts light of the second wavelength and light of the thirdwavelength; and photodetecting means for detecting light of the firstwavelength, light of the second wavelength and light of the thirdwavelength; further comprising: moving means for moving the informationrecording medium and the optical head relative to each other; whereinlight of the first wavelength, light of the second wavelength and lightof the third wavelength pass through the optical element, after whichthey are focused by the focusing means and are irradiated onto theinformation recording media; wherein the first optical element is anoptical element in which grooves are formed in a substrate; wherein theexpression:380 nm≦(n−1)×d≦420 nm is satisfied, where n is a refractive index of thesubstrate at a wavelength of 400 nm, and d (nm) is a depth per step ofthe grooves; wherein the grooves are formed in two steps of depth d anddepth 2 d; wherein when light of a wavelength λ2 in a range of 630 nm to680 nm passes through the grooves, with respect to each of thegrooves..a fractional value smaller than a decimal point of a valueobtained by dividing a light path difference attributable to the groovesby the wavelength λ2 is calculated, and when the calculated fractionalvalues corresponding respectively to the grooves are arranged in anorder in which the grooves are lined up. the fractional values are in anorder ascending or descending in a stepwise manner; and wherein thephotodetecting means detects light that is at least either reflected ordiffracted by the information recording media.
 27. The opticalinformation recording and reproduction apparatus according to claim 26,further comprising: a second optical element that passes light of thefirst wavelength and light of the third wavelength, and diffracts lightof the second wavelength; wherein light of the first wavelength, lightof the second wavelength and light of the third wavelength pass throughthe two optical elements, after which they are focused by the focusingmeans, and irradiated onto the optical information recording medium. 28.An optical head, comprising: a first light source that emits light of afirst wavelength that is in a range of 380 nm to 420 nm and that atleast either records onto or reproduces information from a firstinformation recording medium; a second light source that emits light ofa second wavelength, that at least either records onto or reproducesinformation from a second information recording medium; an opticalelement that passes light of the first wavelength, and converts thephase of light of the second wavelength; focusing means for focusinglight of the first wavelength and light of the second wavelength ontothe information recording medium; and detecting means for detectinglight of the first wavelength and light of the second wavelength;wherein the position of the second light source is set further from thefocusing means than a position that is substantially midway between theposition of that light source at which the aberration at the informationrecording surface of the second information recording medium when theoptical element is not present is at a minimum, and the position of thatlight source at which light of the second wavelength that is incident onthe focusing means is collimated light; wherein the optical element isan optical element comprising a substrate, in which steps are formedprotruding from a flat surface thereof; and wherein the expression:380 nm≦(n−1)×d≦420 nm is satisfied when a refractive index of thesubstrate at a wavelength of 400 nm is n, and a height (nm) of one stepis d.
 29. The optical head according to claim 28, further comprising:tilting means for tilting the focusing means.
 30. The optical headaccording to claim 28, wherein the optical element corrects theaberration to not more than 70 mλ when light of the second wavelength isfocused on the information recording surface of the second informationrecording media.
 31. An optical information recording and reproductionapparatus, comprising: an optical head according to claim 28 and movingmeans for moving the information recording media and the optical headrelative to each other.
 32. A computer, comprising: an opticalinformation recording and reproduction apparatus that includes anoptical head according to claim 28, as an external storage device. 33.An image recording device, comprising: an optical information recordingand reproduction apparatus that includes an optical head according toclaim 28 which can at least record images from among recording imagesonto and reproducing images from an information recording medium.
 34. Animage reproduction device, comprising: an optical information recordingand reproduction apparatus that includes an optical head according toclaim 28 wherein it specializes in reproducing images from aninformation recording medium.
 35. A server, comprising: an opticalinformation recording and reproduction apparatus that includes anoptical head according to claim 4, 9 or 28 as an external storagedevice.
 36. A car navigation system, comprising: an optical informationrecording and reproduction apparatus that includes an optical headaccording to claim 4, 9 or 28 as an external storage device.